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Ionospheric perturbations in plasma parameters before global strong earthquakes
Accepted Manuscript Ionospheric perturbations in plasma parameters before global strong earthquakes Jing Liu, Jianping Huang, Xuemin Zhang PII: DOI: Reference:
S0273-1177(13)00826-0 http://dx.doi.org/10.1016/j.asr.2013.12.029 JASR 11658
To appear in:
Advances in Space Research
Received Date: Revised Date: Accepted Date:
16 September 2013 19 December 2013 20 December 2013
Please cite this article as: Liu, J., Huang, J., Zhang, X., Ionospheric perturbations in plasma parameters before global strong earthquakes, Advances in Space Research (2014), doi: http://dx.doi.org/10.1016/j.asr.2013.12.029
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Ionospheric perturbations in plasma parameters before global strong earthquakes Jing Liua,b,c,*, Jianping Huanga, Xuemin Zhanga a Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China b Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China c University of Chinese Academy of Sciences, Beijing 100049, China
Abstract Based on the electron density (Ne) and temperature (Te) data from DEMETER, the ionospheric perturbations before 82 Ms≥7.0 earthquakes (EQs) during 2005 to 2010 were studied, using moving median and space difference methods within 10 days before and 2 days after these events in local nighttime. It was found that the plasma parameters disturbances appeared before 49 EQs, in which more disturbances were detected before shallow-focus earthquakes than deep ones, and there was little difference between continental and oceanic ones, both exceeding 1/2 percentage. For the disturbed time, more perturbations were seen in 1,3,5,6,8 days before EQs and 1 day after EQs. For the spatial distribution, the anomalies before EQs were not just above the epicenters, but shifted equatorward with several degrees to almost twenty degrees. Most of the abnormities were positive ones, which demonstrate that Ne increases before EQs at the altitude of 670km of DEMETER. Perturbations of Ne were more than that of Te, which illustrates that Ne is much more sensitive to seismic activity than Te.
Key words: Ionospheric perturbations; Abnormities of EQs; DEMETER satellite
1． Introduction Recently, earthquake precursor in the ionosphere is becoming one of the most challenging issues both in earthquake science and ionospheric science field. Based on the analysis of ionospheric data before strong EQs, some perturbations have been found in D, E, F layers respectively over the epicentral areas (Pulinets and Legen‟ka, 1994; Liu et al., 2000; Pulinets et al., 2003; Pulinets et al., 2004a; Zhao et al., 2008; *
Corresponding author. Tel.: +86 10 88015644; fax: +86 10 88015464 E-mail addresses: [email protected] (J. Liu), [email protected] (J. Huang), [email protected] (X. Zhang) 1
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Perrone et al., 2010; Heki, 2011; Le et al., 2012). The seismic research on plasma parameters has been developed quickly due to the rapid growth on the monitoring technologies such as GPS TEC, COSMIC, and satellite in-situ observations (Zhang et al, 2009; Hsiao et al, 2009; Liu et al., 2011), besides the ground-based ionosonde (Sharma et al., 2008; Xu et al., 2010). According to these investigations, it is obtained that seismic ionospheric perturbations always concentratedly occurred in a week before the earthquakes, showing typical imminent precursory feature. And some lithosphere-atmosphere-ionosphere
(LAI)
models,
by
electromagnetic
wave
propagation, acoustic gravity wave and geochemical channel, have been brought out to explain the earthquake-ionosphere coupling process (Pulinets and Boyarchuk, 2004b; Kamogawa, 2006; Hayakawa, 2006). DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) was launched on June 29th, 2004 and ended on December 9th, 2010, which means that there are 6.5 years of data. There were several payloads on this satellite, including electric field instrument, magnetic field instrument, plasma analyzer, Langmuir probe, particle detector instrument (Cussac et al., 2006). With the DEMETER data, many perturbations have been found before some strong EQs, including the electromagnetic field and plasma density before Kii island earthquake (Parrot et al.，2006), EM radiation before Gujarat earthquake (Bhattacharya et al.， 2007), electromagnetic radiation before Wenchuan earthquake (Zeng et al., 2009), ULF & ELF electrostatic perturbations before the 32 EQs (Zhang et al., 2012). As for the plasma parameters, anomalies concentrated 3 days prior to Wenchuan Earthquake, especially the Te variation on 9 May in (Zhang et al., 2010) research. Sarkar et al. (2012) found there was a significant enhancement of electron density and electron temperature near the epicenter, which was detected both in day and night times. Karia et al. (2012) used GPS-based TEC and electron density observed by the DEMETER satellite to analyze Sumatra earthquake on 30 September 2009. Based on ion measurement, Li et al. (2013) searched anomalies with the complete data set of DEMETER satellite, and found the number of good detections increases with the 2
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magnitude of the earthquakes. Most of them have paid attention to the perturbations before specific events, but there are so many data for DEMETER that we intend to study all of strong EQs in this period. For the earthquake monitoring and prediction, it is not enough only to study a few orbits informations, however we need to understand the evolutional features both in temporal series and spatial distribution in order to build their relationship with earthquakes. In this article, Ne and Te, which are detected by the Langmuir probe (ISL) on board of DEMETER satellite (Lebreton et al., 2006), will be analyzed all the global Ms≥7.0 EQs during 2005 to 2010, and some statistical characteristics of the perturbations can be achieved with the EQs, such as the time shift, region relationship, intensity and so on. 2. Earthquake data The Ms≥7.0 EQs (selecting mB for Ms missing) were chosen between January 1st, 2005 and November 31st, 2010 all over the world from the China Earthquake Networks Center (CENC, http://www.csndmc.ac.cn/newweb/data.htm). We used some principles to get earthquakes catalogue for analysis effectiveness. Firstly, EQs within ±65°latitude were selected. Then EQs were omitted if they were within 15 days and 10°away from the previous one in order to avoid the post-seismic effects. Thirdly, those EQs were also omitted if there were no enough Ne/Te data (e.g., more than half data missing) during the 40 days before the EQs. Finally, 82 EQs, as shown in Fig.1, Tab.1, were left, which included 21 continental (C) EQs and 61 oceanic (O) ones. Fig.1. Epicenters location picture of Ms≥7.0 EQs from January 1st, 2005 to November 31st, 2010 (red circles represented greater than Ms7 but less than Ms7.5 EQs; black circles represented greater than Ms7.5 but less than Ms8.0 EQs; green circles represented greater than Ms8.0 EQs.) Tab.1. EQs information table
3. Analytical methods 3
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3.1 Moving median method (MMM) Here the original Ne/Te data along one night side orbit around the epicenter ± 20°were resampled by 0.1°in latitude direction, and then the current background median was calculated using moving method with previous 20 night side orbits (about 10 days) as the calculation window and 1 orbit as the step window, taking 80%, 20% quantile as the upper and lower thresholds at the same time, as shown in Fig.2 (a). In order to stick out the outliers, a new series was produced according to the following definition: if the observation data were higher than upper threshold or lower than lower threshold, the values in the new series should be the differences between observation data and thresholds, otherwise, giving „0‟ to the values in the new series, which were shown by “Subtract_Te” in Fig.2 (b). Then we identified the abnormities if the values in the new series were beyond ±10000 cm-3 for Ne and 500K for Te according to previous analysis results (Liu et al., 2013). Fig.2 (c) illustrated the relative changes by %Dev according to the formula below: Od Ub Ub 100% % Dev 0 Od Lb 100% Lb
Od Ub Lb Od Ub
(1)
Od Lb
In this formula, Od, Ub, Lb were observation data, upper threshold and lower threshold respectively.
Fig.2. MMM analysis of Sumatra earthquake on March 28th, 2005 ( in panel(a), black, red, green and blue lines represent observation data, median value, upper and lower thresholds respectively; panel(b) shown the subtract values; data of panel(c) was calculated by eq(1))
3.2 Space difference method (SDM) Before Samoa islands Ms 8.1 earthquake on September 29th, 2009, some disturbances were detected at the northeastern direction (Fig.3a), and we used space difference method to analyze the data in order to extract the perturbation. Taking the 4
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epicenter as center, ±20°area was divided into 4°(longitude)×2°(latitude) grids. Then the background median (BM) (Fig.3b) and standard deviation (std) (Fig.3c) in each grid were obtained using data between 40 and 10 days before EQs. From 10 days before EQs to 2 days after EQs, we also got observation median (OM) (Fig.3d) for each orbit data falling into each grid, and then the normalization can be from the ratio of the subtract (OM-BM) and the std in each grid with the equation of
SDij
OMij BMj ，in which i=-10,-9,…2, represented the days difference relative std j
to the earthquake; j was the number of grids. In this way, space difference picture for the day on September 29th can be got, shown in Fig.3e, and ±10σ(standard deviation) was selected as the threshold for abnormity. 10 hours before this earthquake, after SDM analyzing, relative to background, Ne of left orbit was normal phenomenon and disturbance of right orbit became more obviously.
Fig.3. Ne spacial picture of 10 hours before Samoa islands Ms 8.1 earthquake on September 29th, 2009 (panel a was the real data on September 29th, 2009; panels b, c were background median and standard deviation from 40 to 10 days before earthquake; panels d, e illustrated observation median and space difference on September 29th, 2009)
4. Results analysis Using the methods of MMM and SDM above, total 82 EQs with Ms≥7.0 were studied. If the abnormity occurred on the day with Dst﹤-30 or Kp≥4- or AE>500 or AL>500 or AU<-500, it would not be considered as an earthquake one. At last, the perturbations in Ne and Te were found before 49 EQs, and after 3 EQs, while no obvious disturbances were exhibited around 30 EQs. The detailed information on abnormities
before
49
EQs
were
listed
in
Tab.2,
including
earthquake
information(date, longitude and latitude), the amplitude, distance, direction, occurrence time and character of the anomalies, method used and earthquake type (oceanic or continental).
5
Tab.2. Characteristics of abnormities before 49 EQs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
4.1 Abnormal features corresponding to different EQs types According to the epicentral locations, all 82 EQs were divided into continental EQs and oceanic EQs. The total number of different EQs types, EQs number with abnormities and their percentages were listed in Tab.3. As you can see, 61 EQs in 82 were oceanic ones, and there were 37 EQs with ionospheric anomalies in it, occupying 60.7%, which was litter greater than the continental EQs with 57.1% by 12/21. Whatever continental or oceanic earthquakes, precursors were both detected in more than 1/2 large events, which may be explained by the radon emanating theory (Pulinets et al., 2006). The radon would emanate from the Earth‟s crust during the earthquake preparation process, and changes the air conductivity and the atmospheric electric field through the formation of large ion clusters over the epicentral area. Maybe the different media of continent and ocean decide the difficulty of radon overflow to atmosphere. According to the focus depth, they were divided into deep EQs (deeper than 70km) and shallow EQs. As shown in Tab. 3, the percent of earthquakes with anomalies before shallow EQs was much higher by 62.0% than that of 45.4% before deep ones. As for the shallow earthquakes, many micro-fractures would be formed near the surface due to accumulation of stress in the seismogenic zone, along which chemical materials such as radon and aerosols would gather, and electromagnetic emissions would propagate easily into the atmosphere and then to the ionosphere, so it can sort of understand that perturbations produced at shallow depth can be much easily detected in ionosphere than those from the deep focus.
Tab.3. Total numbers, abnormal numbers and probability of different types EQs
4.2 The temporal characteristics of plasma anomalies related to earthquakes Based on Tab.2, we summed the occurrence time of each anomaly according to the days before EQs, and if the perturbations for one parameter occurred in approximately same area at the same day by using two methods, it would be considered being only one. From Fig.4, abnormities almost appeared every day from 10 days before EQs to 2 days after EQs, but in 1, 3, 5, 6, 8 days before EQs their 6
occurrence was higher, exceeding median value 11.5, which illustrate that the number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
of anomalies in ionosphere increased in 8 days before EQs, especially in 6, 5 days. Hasbi et al. (2011) investigated the ionospheric variations before four earthquakes with M≥7.9 taking place during 2004-2007 in Sumatra by using GPS and CHAMP data, and their result showed the occurrence of anomalies detected within a few hours to 6 days before the earthquakes. Using GPS TEC data, Liu et al. (2004) found that the seismo-ionospheric precursors were detected 1-5 days prior to 20 major earthquakes in Taiwan. So our results in temporal distribution of plasma anomalies were consistent with others. However, in our research, the biggest number of anomalies occurred just one day after the EQs, not only concentrated before the EQs, which may be related to the occurrence of amount of aftershocks at seismic regions.
Fig.4. Abnormity numbers in each day before EQs
4.3 The spatial distribution feature of plasma perturbations The abnormity numbers in eight directions were summed based on direction column in Tab.2, and if the abnormities appeared in 2 or more directions, each direction would be recorded separately. As shown in Tab.4, for EQs in the geomagnetic north hemisphere, the abnormity numbers were 29 in sum of SE, S, SW, larger than 18 in sum of NW, N, NE directions. For EQs in the geomagnetic south hemisphere, the perturbations were more often located at the north of the epicenters with the sum number of 63 than 32 at their south. The abnormal regions in the ionosphere before EQs were not just above the epicenters, but shifted equatorward with a distance of several degrees to almost twenty degrees. This feature has been demonstrated in other plasma parameters, such as GPS TEC with perturbations occurring at the southeast of the epicenter and its conjugate area at the southern hemisphere on May 9, 3 days before the Wenchuan earthquake in 2008 (Zhao et al., 2008). Tab.4. Abnormal numbers in each direction
Pulinets et al. (2004b) considered this phenomenon was caused by ionospheric particles E×B drift in anomalous electric field penetrating from ground. Kuo et al. (2011) proposed the electrical coupling between ionosphere and surface charges in 7
earthquake fault zone, and they thought the vertical surface electric field drove the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
current in atmosphere and electric field at the bottom of the ionosphere. Whether penetration or secondary electric field in the ionosphere, it moved upward to satellite altitude along the magnetic lines, causing E × B motion, and leading to electron movement to equatorward and also to east and west directions under down and up electric field.
4.4 Comparison of two parameters Besides the same abnormities using different analysis methods, there were 131 records separately on Te or Ne, among which the number of Ne (106) were more than that of Te (25), which illustrate that Ne is much more sensitive to seismic activity than Te. The synchronous abnormities of Ne and Te were only 2 times, including 1 positive correlations and 1 negative correlation. Because of the small synchronous abnormity samples, no statistical regularity can be obtained between Ne and Te before EQs in our study. 4.5 Abnormal characters in shape As shown in Tab. 2, there were 97 positive and 9 negative abnormities in Ne, and for Te, there were 19 positive and 6 negative abnormities respectively. Whatever Ne or Te, positive abnormities were more than negative ones. Liu et al. (2009) found that TEC (total electron content) reduced at southeast on May 6 and increased at southeast on May 9 before Wenchuan earthquake. Yao et al. (2012) also found that both positive and negative anomalies were likely to occur before earthquakes by analyzing GIM TEC before the global M=7.0+ earthquakes in 2010. In other word, electromagnetic environment in the ionosphere has been significantly changed over different EQs or different time of same EQs, so positive and negative abnormities can both appear before EQs, but with our statistics results, positive anomalies may occur more frequently at the altitude of DEMETER satellite of 670 km. 5. Conclusions Based on the analysis of Ne and Te data detected by DEMETER satellite in local nighttime, the ionosphere perturbations before 49 Ms≥7.0 EQs during 2005 to 2010 have been distinguished using moving median and space difference methods within 8
10 days before and 2 days after. Summing up the temporal, spatial distribution 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
characteristics of these anomalies, and their relationship to different type of earthquakes, it can be concluded as follows: 1)
More perturbations in Ne and Te were seen in 1, 3, 5, 6, 8 days before the EQs and 1 day after the EQs.
2)
The ionospheric anomalies always shifted equatorward with several degrees to almost twenty degrees, which may be related to the effect of E×B drift due to the anomalous electric field over the epicentral area.
3)
More disturbances were detected before shallow-focus earthquakes than deep ones. And there was little difference between continental and oceanic ones, both exceeding 1/2 percentage.
4)
Most of the abnormities were positive ones, which demonstrate that Ne increases before EQs at the altitude of 670km of DEMETER.
5)
Perturbations of Ne occurred more often than those of Te, which illustrate that Ne is much more sensitive to seismic activity than Te.
Acknowledgements This work is supported by the National Natural Science Foundation of China (41204109, 41104030) and the National High-Tech Research and Development Program of China (863 Program) (2012AA121004). The authors acknowledge DEMETER satellite center for providing the level 1 data and CENC for providing the down loading earthquake catalogue. .
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Table
UT 2005/01/01 06:25 2005/01/19 06:11 2005/02/26 12:56 2005/03/02 10:42 2005/03/20 01:53 2005/03/28 16:09 2005/05/14 05:05 2005/06/13 22:44 2005/06/15 02:50 2005/07/05 01:52 2005/07/24 15:42 2005/08/16 02:46 2005/09/09 07:26 2005/09/26 01:55 2005/11/14 21:38 2006/02/22 22:19 2006/04/20 23:25 2006/05/03 15:26 2006/05/16 10:39 2006/05/16 15:28 2006/05/22 11:11 2006/07/17 08:19 2006/11/15 11:14 2007/01/21 11:27 2007/03/25 00:39 2007/03/25 00:41 2007/04/01 20:39 2007/07/16 10:13 2007/08/01 17:08 2007/09/12 11:10 2007/11/14 15:40 2007/12/09 07:28 2008/01/05 11:01 2008/02/08 09:38 2008/02/20 08:08 2008/03/20 22:32 2008/04/09 12:46 2008/05/02 01:33 2008/05/07 16:45 2008/05/12 06:28 2008/06/13 23:43 2008/07/05 02:12 2008/07/19 02:39 2008/09/08 18:52 2008/09/10 13:08 2008/09/11 00:20 2008/09/29 15:19 2008/10/05 15:52 2008/10/19 05:10 2008/11/16 17:02 2009/01/03 19:43 2009/01/15 17:49 2009/02/11 17:34 2009/02/18 21:53
Tab.1. EQs information table Latitude(°) Longitude(°) Magnitude(Ms) 92.25 141.62 95.62 130.16 130.38 97.05 98.40 -69.11 -126.00 97.23 92.19 141.89 153.79 -76.40 144.53 33.10 167.48 -173.72 -179.30 97.04 166.22 107.40 153.27 126.77 170.31 137.47 157.00 138.91 167.65 101.41 -70.20 -177.50 -130.80 -41.90 95.89 81.54 169.88 -178.11 141.26 103.42 141.29 152.95 141.91 167.01 -38.70 143.78 -177.03 73.67 -173.35 122.45 132.90 154.65 126.68 -175.70
4.72 34.00 2.93 -6.70 33.70 2.03 0.34 -19.41 41.30 1.54 7.83 38.15 -4.38 -5.70 38.33 -20.87 60.97 -19.76 -31.80 -0.10 60.77 -9.30 46.69 0.23 -21.28 37.14 -8.50 37.42 -14.98 -4.90 -22.03 -26.00 51.30 10.70 2.54 35.64 -19.86 52.14 36.24 31.01 38.91 53.83 37.56 -13.03 8.10 41.90 -29.46 39.58 -21.32 1.12 -0.40 47.08 3.40 -26.94
7.1 7.0 7.0 7.0 7.3 8.6 7.0 7.8 7.3 7.2 7.6 7.2 7.0 7.6 7.3 7.6 8.3 7.9 7.5 7.3 7.5 7.4 8.0 7.5 7.2 7.2 7.9 7.0 7.0 8.6 7.9 7.5 7.0 7.3 7.7 7.5 7.2 7.0 7.2 8.2 7.3 7.4 7.2 7.2 7.0 7.3 7.1 7.0 7.0 7.0 7.4 7.3 7.4 7.3
Depth(km) 28 37 33 228 21 34 51 115 10 33 19 30 95 115 11 22 32 54 151 22 17 34 9 22 34 8 10 42 145 25 60 152 10 9 30 21 40 16 31 14 7 636 22 129 10 33 26 27 21 30 23 36 30 18
Type O O O O C O O C O C O O O C O C C O O O C O O O O C O C O O C O O O O C O O O C C O O O O O O C O C C O O O
-174.70 -26.80 -86.20 166.41 -112.90 138.02 92.78 99.60 107.30 -171.57 166.82 157.40 -72.50 128.65 -72.80 100.77 -73.20 -115.30 97.20 96.59 100.96 91.91 136.60 -170.21 150.40 123.86 168.01 141.67
2009/03/19 18:17 2009/04/16 14:57 2009/05/28 08:24 2009/07/15 09:22 2009/08/03 17:59 2009/08/09 10:55 2009/08/10 19:55 2009/08/16 07:38 2009/09/02 07:55 2009/09/29 17:48 2009/10/07 22:03 2010/01/03 22:36 2010/01/12 21:53 2010/02/26 20:31 2010/02/27 06:34 2010/03/05 16:06 2010/03/16 02:21 2010/04/04 22:40 2010/04/06 22:15 2010/04/13 23:49 2010/05/05 16:28 2010/06/12 19:26 2010/06/16 03:16 2010/07/18 05:56 2010/07/18 13:04 2010/07/23 22:51 2010/08/10 05:23 2010/08/13 21:19
-23.00 -60.20 16.70 -45.74 29.00 33.12 14.22 -1.95 -7.80 -14.80 -12.68 -8.80 18.50 25.86 -35.80 -4.37 -36.20 32.10 2.31 33.22 -4.84 7.85 -2.20 52.92 -6.00 5.98 -17.05 12.43
7.7 7.0 7.6 7.7 7.3 7.1 7.7 7.1 7.2 8.1 7.8 7.3 7.7 7.3 8.8 7.2 7.0 7.5 7.9 7.3 7.0 7.6 7.3 7.0 7.2 7.1 7.3 7.0
34 20 10 4 6 299 25 45 49 16 38 25 10 25 35 26 18 10 34 14 27 31 18 10 47 594 30 6
O O O O O O O O O O O O O O C O O C O C O O C O C O O O
Tab.2. Characteristics of abnormities before 49 EQs Nu m
Earthquake information
1 2
2005.2.26(95.62, 2.93) 2005.3.20(130.38, 33.7)
Par am ete r Ne Ne Ne Ne
Amplitu de
Distance
Direction
Time
Characte r
method
Ty pe
- 45% +110% +55%
southeast, northeast southwest southwest southwest
2.23(-3) 3.12(-8) 3.15(-5) 3.16(-4)
decrease increase increase increase
MMM MMM MMM SDM
O C
≥10σ
21° -17° 19.2°-23.5° 23.9°-24.9° 13.4°-15.2°
Ne
≥10σ
7°
southwest
3.20(+10 h)
increase
SDM
Ne
≥ 10σ
13.2°-15.2°
south
3.22(+2)
increase
SDM
23.5°-34.7° 14° 11°
Southwest, northwest east northwest
3.21(-7) 3.22(- 6) 3.22(- 6)
decrease decrease increase
MMM MMM SDM
O
northeast north southeast, northeast east, northeast east
6.30(-5) 7.4(-1) 7.5(+13h) 7.7(+2) 7.7(+2)
increase increase increase increase increase
MMM MMM MMM MMM SDM
C
decrease
SDM
O
decrease increase increase
MMM MMM SDM
O
3
2005.3.28(97.05, 2.03)
Ne Te Ne
-50% -38%
4
2005.7.5(97.23, 1.54)
Ne Ne Ne Ne Ne
+ 120% +45% +140% +120% ≥10σ
18.1° -21.7° 3.7°-13.5° 20° -15.7° 19.5° -23.8° 18°
5
2005.7.24(92.19,7.83)
Ne
≤-10σ
14.3°
northeast
6
2005.9.9（153.79,-4.38）
Te Ne Ne
-30% +250%
33.5° 24.5°-27° 27.8°
northwest northeast northeast
7.24(before a few minutes) 7.25(+1) 8.30(-10) 8.30(-10)
Ne Ne
+70%
5.7°-21° 4°-6°
south, north north
8.30(-10) 8.30(-10)
increase increase
MMM SDM
Ne Ne
+70%
4°-5° 18°
east southeast
9.23(-3) 9.23(-3)
increase increase
MMM SDM
Ne Ne
+70% ≥10σ
18.7°-27.7° 13-22°
northeast southwest
9.24(-2) 9.25(-1)
increase increase
MMM SDM
2005.11.14 (144.53,38.33)
Ne
≤-10σ
18.1°
southwest
11.8(-6)
decrease
MMM
O
+25%
2006.2.22(33.1,-20.87)
Te Ne
11.1°- 24.5° in 2.2°
northwest northeast
11.16(+2) 2.17(-5)
increase increase
MMM SDM
C
7
8 9
2005.9.26(-76.4,-5.7)
≥10σ
≥10σ ≥10σ ≥10σ
≥10σ
C
10
2006.7.17 (107.4,-9.3)
Te Ne Te Ne
+ 30% +80% +35%
11
2007.1.21(26.77,0.23)
+45% +60%
12
2007.3.25(137.47,37.14)
Ne Ne Ne
13
2007.4.1(157,-8.5)
+70% +50%
14
2007.7.16(138.91,37.42)
Ne Ne Ne
15
2007.8.1(167.65,-14.98)
Ne Ne
+150%
Ne Ne
+50%
Ne Ne Ne Te Ne
+120% +120% +120% +30%
Ne Ne
+ 45%
16
2007.9.12(101.41,-4.9)
17
2007.11.14(-70.2,-22.03)
18
2007.12.9(-177.5,-26)
19
2008.5.2(-178.11,52.14)
20
2008.7.19(141.91,37.56)
21
2008.9.8 (167.01,-13.03)
12°-14.2° 29.3°-30.3° 17.6°-25.1° 19.3°
southeast southeast southeast southwest
7.13(-4) 7.15(-2) 7.16(-1) 7.17(+8 h)
increase increase increase increase
MMM MMM MMM SDM
O
20.6°-21.5° 19.3°-25.7° 27.7°
southeast southeast southeast
1.11(-10) 1.21(+1) 3.20(-5)
increase increase increase
MMM MMM SDM
O
9.7°to 17.4° 17.3°- 24.9° 17.8°, 21.3°-24.4° 13.9°-20.8° 20°
northeast northwest southeast
3.29(-3) 3.29(-3) 7.7(-9)
increase increase increase
MMM MMM SDM
O
northeast northeast
7.24(-8) 7.24(-8)
increase increase
MMM SDM
O
16° 14°
northeast northeast
9.8(-4) 9.8(-4)
increase increase
MMM SDM
O
12.9°-21.3° 22.2°-25.9° 21.3° -26.4° 15.9° -20.5° 27.8°
southeast, northeast northeast northeast southwest northwest
11.13(-1) 11.15(+1) 11.29(-10) 11.30(-9) 12.1(-8)
increase increase increase increase increase
MMM MMM MMM MMM SDM
C
≥10σ
20.7° -24.1° 18.1° -18.4°
northwest west
12.3(-6) 12.4(-5)
increase increase
MMM SDM
Ne
≥10σ
26.6°
southwest
12.5(-4)
increase
SDM
Ne
≥10σ
24.4° -26.1°
southwest
12.8(-1)
increase
SDM
Ne
≥10σ
26.2°
northwest
4.22(-10)
increase
SDM
Te Te Te
+26% +18%
17.6° -17.8° 21.1° -25.8° 26.2°
northeast northwest northwest
4.25(-7) 4.25(-7) 4.25(-7)
increase increase increase
MMM MMM SDM
Te Te Ne Ne
+25% +30% +145%
12.5° -15.1° 21.9° -22.7° 21° -26.4° 16.6°
northwest northeast northeast northeast
7.15(-4) 7.17(-2) 8.30(-9) 8.31(-8)
increase increase increase increase
MMM MMM MMM SDM
Ne Ne
+ 60% ≥10σ
23.1° -24.4° 6.3° -18.1°
northeast north
9.2(-6) 9.2(-6)
increase increase
MMM SDM
Ne
≥10σ
22°, 12.8° -15.6°
northeast, northwest
9.3(-5)
increase
SDM
Ne Ne
+100% ≥10σ
19.4° -20.3° 17.2° -24.4°
northeast northwest
9.9(+1) 9.10(+2)
increase increase
MMM SDM
≥10σ
≥10σ
≥10σ ≥10σ ≥10σ
≥10σ
≥10σ
≥10σ
C
C
O
O
O O
22
2008.9.10(-38.7,8.1)
Ne
≥10σ
25.6°
southwest
9.10(-11h)
increase
SDM
O
23 24
2008.9.29(-177.03,-29.46) 2008.10.5(73.67,39.58)
Ne Ne Ne
+70% +80%
20° -21.5° 17.1° -22.5° 17.2° -20.6°
northeast southeast southeast
9.21(-8) 9.25(-10) 9.25(-10)
increase increase increase
MMM MMM SDM
O C
Ne Ne
+75% ≥10σ
28.3° -32.4° 16.1° -20.1°
southeast south
10.6(+1) 10.6(+1)
increase increase
MMM SDM
Ne
≥10σ
18.7°
southeast
10.16(-3)
increase
SDM
O
26
2008.10.19(-173.35,-21.32 ) 2008.11.16 (122.45,1.12)
Ne
≥10σ
19°-20.6°
southwest
11.14(-2)
increase
SDM
C
27
2009.2.11(126.68,3.4)
Ne
≥10σ
17°
north
2.6(-5)
increase
SDM
O
28
2009.2.18(-175.7,-26.94)
Ne
≥10σ
25.1°-28.4°
southwest
2.10(-8)
increase
SDM
O
Te
≤-10σ
25.1°-28.4°
southwest
2.10(-8)
decrease
SDM
Ne Te Ne Te Ne Ne Ne Te Te Te Te Ne
+80% +35% +60% +28% +65% +60% +80% +28% +25% +25% +30%
northeast southwest north southwest north northeast southeast, northeast northwest northwest northwest northeast south
2.11(-7) 2.11(-7) 2.13(-5) 2.13(-5) 2.16(-2) 3.16(-3) 5.19(-9) 5.23(-5) 5.26(-2) 7.27(-7) 7.31(-2) 8.5(+2)
increase increase increase increase increase increase increase increase increase increase increase increase
MMM MMM MMM MMM MMM MMM MMM MMM MMM MMM MMM SDM
O O
25
≥10σ
29 30
2009.3.19(-174.7,-23.0) 2009.5.28(-86.2,16.7)
31
2009.8.3(-112.9,29)
≥10σ
17.8°-23.4° 8.7°-13.7° 16.5°-20.2° 22.4°-23.4° 5.9°-9.2° 11° 24.8°-20.6° 17.5°-24.4° 19.7°-23.3° 16.1°-17.7° 13.1°-18.8° 13°
32
2009.8.10(92.78,14.22)
Ne
≥10σ
11.7°-17.1°
northwest
7.31(-10)
increase
SDM
O
33
2009.8.16 (99.6,-1.95)
Ne
≤10σ
17.8°
southwest
8.8(-8)
decrease
SDM
O
Ne
≥10σ
18.4°-15.2°
southeast, northeast
8.10(-6)
increase
SDM
Ne
≥10σ
19°-21.6°
northeast
8.16(+6h)
increase
SDM
Ne
≥10σ
9°
north
8.24(-9)
increase
SDM
Ne Ne
+100% ≥10σ
12.9°-21.9° 12.8°-14.5°
northeast northeast
8.29(-4) 8.29(-4)
increase increase
MMM SDM
Ne
≥10σ
2.2°
northwest
9.3(+1)
increase
SDM
34
2009.9.2 (107.3,-7.8)
O
O
35
2009.9.29 (-171.57,-14.8)
36
2009.10.7 (166.82,-12.68)
37
2010.1.3(157.4,-8.8)
38
2010.1.12(-72.5,18.5)
39
2010.2.26(128.65,25.86)
40
2010.2.27(-72.8,35.8)
41
2010.3.5(100.77,-4.37)
Ne Ne
+120%
Ne
≥10σ
Ne
≥10σ
Ne Ne Ne Ne
+160% +70% +170% +58%, +60% -27% +145%
≥10σ
Te Ne Ne
≥10σ
Te Te Ne Ne
-26% +28% +95%
Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne
+60% +70% -45% +40% +100% +90% -43% +37% +35% +110% +55% +130% +25% +70%
≥10σ
≥10σ
7.4°-20.2° 6.7°-9.2°
northeast northeast
9.24(-5) 9.24(-5)
increase increase
MMM SDM
O
18.2°-19.2°,12.2° -14.9° 18.0°-19.3°
northeast, northwest
9.26(-3)
increase
SDM
northeast
9.29 (-10h)
increase
SDM
10.8°-20.3° 19.2° 19.6°-24.9° 17.9° and 11.6°
northeast northeast southeast, northeast southeast
9.30(-7) 10.2(-5) 10.5(-2)
MMM MMM MMM MMM
O
1.3（-12h）
increase increase increase increase
26.8°- 31.3° 26.1°- 33.4° 10.2°- 11.7°
northwest southeast southwest
1.2(-10) 1.3(-9) 1.4(-8)
decrease increase increase
MMM MMM SDM
O
24.2°- 25.4° 18.1° 15.4°- 21.4° 13.4°- 17.1°
northeast northeast southeast southeast
1.6(-6) 1.11(-1) 1.12(-19h) 1.12(-19h)
decrease increase increase increase
MMM MMM MMM SDM
27.4°- 31.9° 20.1°-3.4° 23.8° -27.2° 19°-24.8° 12.2°-20° 14.3°-19.4° 12.7°-15.1° 4.9° 30° 22.6° -25.4° 17.8°
southeast southeast, northwest southeast southwest southeast southwest northeast northwest northwest southeast, northeast northwest
1.13(+1) 2.19(-7) 2.20(-6) 2.21(-5) 2.27(+1) 2.27(+1) 2.24(-3) 2.26(-1) 2.26(-1) 2.27(-6) 3.3(-2)
increase increase decrease increase increase increase decrease increase increase increase increase
MMM MMM MMM MMM MMM MMM MMM MMM MMM MMM SDM
southeast, northeast northwest southeast northeast northeast
3.6(+1) 3.8(-8) 3.17(+1) 3.18(+2) 3.31(-6)
increase increase increase increase decrease
MMM MMM MMM MMM SDM
O
O
C
O
42
2010.3.16(-73.2,-36.2)
43
2010.4.6(97.2,2.31)
Ne Ne Te Ne Te
≤10σ
16.6° to 15.9° 15.7° -22.8° 30.8°-37.5° 19.7° -23.1° 3.6°
44
2010.5.5(100.96,-4.84)
Ne
≤10σ
20.5°
northeast
4.27(-8)
decrease
SDM
O
2010.6.16(136.6,-2.2)
Ne Ne Ne
+50% +70%
18.9°-24.1° 11.2° to 23° 6.7°
northeast northwest southwest
4.30(-5) 6.13(-3) 6.13(-3)
increase increase increase
MMM MMM SDM
C
Te Te Ne
+20% +28%
15.5°-16.5° 22.7° -23.1° 6.7°
east southeast southeast
7.10(-8) 7.16(-2) 7.12(-6)
increase increase decrease
MMM MMM SDM
Te Ne Ne
+30% +100%
25.8° -27.7° 16.5° -21.9° 16.2°
southwest northwest northwest
7.16(-2) 7.31(-10) 7.31(-10)
increase increase increase
MMM MMM SDM
Ne Ne Ne
+70% +70%
17.2° -23.2° 20.2° -23.7° 21.3° -24.4°
northeast northwest northwest
8.7(-3) 8.7(-3) 8.7(-3)
increase increase increase
MMM MMM SDM
Ne Ne
+150%
24.7° -24.2° 18.0°
southeast, northeast southeast
8.10(+4h) 8.12(+2)
increase increase
MMM SDM
Ne Ne Ne
+100% +100%
increase increase increase
MMM MMM SDM
≥10σ
southeast southwest, northwest east, southwest, northwest southwest
8.7(-6) 8.7(-6) 8.7(-6)
Ne
15.9°-18.6° 17.5° -16.4° 10°-10.8°,15.2°14.6° 14.3°
8.14(+1)
increase
SDM
45 46
2010.7.18(-170.21,52.92)
47
2010.7.18(150.4,-6)
48
49
2010.8.10(168.01,-17.05)
2010.8.13(141.67,12.43)
≥10σ
≤10σ
≥10σ
≥10σ ≥10σ
≥10σ
O
O
O C O
O
Annotation: Distance of SDM was calculated from epicenter to abnormal grid center; Distance of MMM was calculated from epicenter to start and end abnormal spots, and amplitude indicated the difference between observation data and threshold for the peak in this orbit.
Tab.3. Total numbers, abnormal numbers and probability of different types EQs Type Numbers Earthquake numbers Abnormal numbers Percentage
Continental EQs
Oceanic EQs
Deep EQs
Shallow EQs
21 12
61 37
11 5
71 44
57.1％
60.7％
45.4％
62.0％
Tab.4. Abnormal numbers in each direction
Direction Numbers Magnetic north EQs Magnetic south EQs
E
SE
S
SW
W
NW
N
NE
2 2
14 19
3 1
12 12
0 1
10 18
0 7
8 38
S0273-1177(13)00826-0 http://dx.doi.org/10.1016/j.asr.2013.12.029 JASR 11658
To appear in:
Advances in Space Research
Received Date: Revised Date: Accepted Date:
16 September 2013 19 December 2013 20 December 2013
Please cite this article as: Liu, J., Huang, J., Zhang, X., Ionospheric perturbations in plasma parameters before global strong earthquakes, Advances in Space Research (2014), doi: http://dx.doi.org/10.1016/j.asr.2013.12.029
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Ionospheric perturbations in plasma parameters before global strong earthquakes Jing Liua,b,c,*, Jianping Huanga, Xuemin Zhanga a Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China b Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China c University of Chinese Academy of Sciences, Beijing 100049, China
Abstract Based on the electron density (Ne) and temperature (Te) data from DEMETER, the ionospheric perturbations before 82 Ms≥7.0 earthquakes (EQs) during 2005 to 2010 were studied, using moving median and space difference methods within 10 days before and 2 days after these events in local nighttime. It was found that the plasma parameters disturbances appeared before 49 EQs, in which more disturbances were detected before shallow-focus earthquakes than deep ones, and there was little difference between continental and oceanic ones, both exceeding 1/2 percentage. For the disturbed time, more perturbations were seen in 1,3,5,6,8 days before EQs and 1 day after EQs. For the spatial distribution, the anomalies before EQs were not just above the epicenters, but shifted equatorward with several degrees to almost twenty degrees. Most of the abnormities were positive ones, which demonstrate that Ne increases before EQs at the altitude of 670km of DEMETER. Perturbations of Ne were more than that of Te, which illustrates that Ne is much more sensitive to seismic activity than Te.
Key words: Ionospheric perturbations; Abnormities of EQs; DEMETER satellite
1． Introduction Recently, earthquake precursor in the ionosphere is becoming one of the most challenging issues both in earthquake science and ionospheric science field. Based on the analysis of ionospheric data before strong EQs, some perturbations have been found in D, E, F layers respectively over the epicentral areas (Pulinets and Legen‟ka, 1994; Liu et al., 2000; Pulinets et al., 2003; Pulinets et al., 2004a; Zhao et al., 2008; *
Corresponding author. Tel.: +86 10 88015644; fax: +86 10 88015464 E-mail addresses: [email protected] (J. Liu), [email protected] (J. Huang), [email protected] (X. Zhang) 1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Perrone et al., 2010; Heki, 2011; Le et al., 2012). The seismic research on plasma parameters has been developed quickly due to the rapid growth on the monitoring technologies such as GPS TEC, COSMIC, and satellite in-situ observations (Zhang et al, 2009; Hsiao et al, 2009; Liu et al., 2011), besides the ground-based ionosonde (Sharma et al., 2008; Xu et al., 2010). According to these investigations, it is obtained that seismic ionospheric perturbations always concentratedly occurred in a week before the earthquakes, showing typical imminent precursory feature. And some lithosphere-atmosphere-ionosphere
(LAI)
models,
by
electromagnetic
wave
propagation, acoustic gravity wave and geochemical channel, have been brought out to explain the earthquake-ionosphere coupling process (Pulinets and Boyarchuk, 2004b; Kamogawa, 2006; Hayakawa, 2006). DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) was launched on June 29th, 2004 and ended on December 9th, 2010, which means that there are 6.5 years of data. There were several payloads on this satellite, including electric field instrument, magnetic field instrument, plasma analyzer, Langmuir probe, particle detector instrument (Cussac et al., 2006). With the DEMETER data, many perturbations have been found before some strong EQs, including the electromagnetic field and plasma density before Kii island earthquake (Parrot et al.，2006), EM radiation before Gujarat earthquake (Bhattacharya et al.， 2007), electromagnetic radiation before Wenchuan earthquake (Zeng et al., 2009), ULF & ELF electrostatic perturbations before the 32 EQs (Zhang et al., 2012). As for the plasma parameters, anomalies concentrated 3 days prior to Wenchuan Earthquake, especially the Te variation on 9 May in (Zhang et al., 2010) research. Sarkar et al. (2012) found there was a significant enhancement of electron density and electron temperature near the epicenter, which was detected both in day and night times. Karia et al. (2012) used GPS-based TEC and electron density observed by the DEMETER satellite to analyze Sumatra earthquake on 30 September 2009. Based on ion measurement, Li et al. (2013) searched anomalies with the complete data set of DEMETER satellite, and found the number of good detections increases with the 2
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
magnitude of the earthquakes. Most of them have paid attention to the perturbations before specific events, but there are so many data for DEMETER that we intend to study all of strong EQs in this period. For the earthquake monitoring and prediction, it is not enough only to study a few orbits informations, however we need to understand the evolutional features both in temporal series and spatial distribution in order to build their relationship with earthquakes. In this article, Ne and Te, which are detected by the Langmuir probe (ISL) on board of DEMETER satellite (Lebreton et al., 2006), will be analyzed all the global Ms≥7.0 EQs during 2005 to 2010, and some statistical characteristics of the perturbations can be achieved with the EQs, such as the time shift, region relationship, intensity and so on. 2. Earthquake data The Ms≥7.0 EQs (selecting mB for Ms missing) were chosen between January 1st, 2005 and November 31st, 2010 all over the world from the China Earthquake Networks Center (CENC, http://www.csndmc.ac.cn/newweb/data.htm). We used some principles to get earthquakes catalogue for analysis effectiveness. Firstly, EQs within ±65°latitude were selected. Then EQs were omitted if they were within 15 days and 10°away from the previous one in order to avoid the post-seismic effects. Thirdly, those EQs were also omitted if there were no enough Ne/Te data (e.g., more than half data missing) during the 40 days before the EQs. Finally, 82 EQs, as shown in Fig.1, Tab.1, were left, which included 21 continental (C) EQs and 61 oceanic (O) ones. Fig.1. Epicenters location picture of Ms≥7.0 EQs from January 1st, 2005 to November 31st, 2010 (red circles represented greater than Ms7 but less than Ms7.5 EQs; black circles represented greater than Ms7.5 but less than Ms8.0 EQs; green circles represented greater than Ms8.0 EQs.) Tab.1. EQs information table
3. Analytical methods 3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
3.1 Moving median method (MMM) Here the original Ne/Te data along one night side orbit around the epicenter ± 20°were resampled by 0.1°in latitude direction, and then the current background median was calculated using moving method with previous 20 night side orbits (about 10 days) as the calculation window and 1 orbit as the step window, taking 80%, 20% quantile as the upper and lower thresholds at the same time, as shown in Fig.2 (a). In order to stick out the outliers, a new series was produced according to the following definition: if the observation data were higher than upper threshold or lower than lower threshold, the values in the new series should be the differences between observation data and thresholds, otherwise, giving „0‟ to the values in the new series, which were shown by “Subtract_Te” in Fig.2 (b). Then we identified the abnormities if the values in the new series were beyond ±10000 cm-3 for Ne and 500K for Te according to previous analysis results (Liu et al., 2013). Fig.2 (c) illustrated the relative changes by %Dev according to the formula below: Od Ub Ub 100% % Dev 0 Od Lb 100% Lb
Od Ub Lb Od Ub
(1)
Od Lb
In this formula, Od, Ub, Lb were observation data, upper threshold and lower threshold respectively.
Fig.2. MMM analysis of Sumatra earthquake on March 28th, 2005 ( in panel(a), black, red, green and blue lines represent observation data, median value, upper and lower thresholds respectively; panel(b) shown the subtract values; data of panel(c) was calculated by eq(1))
3.2 Space difference method (SDM) Before Samoa islands Ms 8.1 earthquake on September 29th, 2009, some disturbances were detected at the northeastern direction (Fig.3a), and we used space difference method to analyze the data in order to extract the perturbation. Taking the 4
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
epicenter as center, ±20°area was divided into 4°(longitude)×2°(latitude) grids. Then the background median (BM) (Fig.3b) and standard deviation (std) (Fig.3c) in each grid were obtained using data between 40 and 10 days before EQs. From 10 days before EQs to 2 days after EQs, we also got observation median (OM) (Fig.3d) for each orbit data falling into each grid, and then the normalization can be from the ratio of the subtract (OM-BM) and the std in each grid with the equation of
SDij
OMij BMj ，in which i=-10,-9,…2, represented the days difference relative std j
to the earthquake; j was the number of grids. In this way, space difference picture for the day on September 29th can be got, shown in Fig.3e, and ±10σ(standard deviation) was selected as the threshold for abnormity. 10 hours before this earthquake, after SDM analyzing, relative to background, Ne of left orbit was normal phenomenon and disturbance of right orbit became more obviously.
Fig.3. Ne spacial picture of 10 hours before Samoa islands Ms 8.1 earthquake on September 29th, 2009 (panel a was the real data on September 29th, 2009; panels b, c were background median and standard deviation from 40 to 10 days before earthquake; panels d, e illustrated observation median and space difference on September 29th, 2009)
4. Results analysis Using the methods of MMM and SDM above, total 82 EQs with Ms≥7.0 were studied. If the abnormity occurred on the day with Dst﹤-30 or Kp≥4- or AE>500 or AL>500 or AU<-500, it would not be considered as an earthquake one. At last, the perturbations in Ne and Te were found before 49 EQs, and after 3 EQs, while no obvious disturbances were exhibited around 30 EQs. The detailed information on abnormities
before
49
EQs
were
listed
in
Tab.2,
including
earthquake
information(date, longitude and latitude), the amplitude, distance, direction, occurrence time and character of the anomalies, method used and earthquake type (oceanic or continental).
5
Tab.2. Characteristics of abnormities before 49 EQs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
4.1 Abnormal features corresponding to different EQs types According to the epicentral locations, all 82 EQs were divided into continental EQs and oceanic EQs. The total number of different EQs types, EQs number with abnormities and their percentages were listed in Tab.3. As you can see, 61 EQs in 82 were oceanic ones, and there were 37 EQs with ionospheric anomalies in it, occupying 60.7%, which was litter greater than the continental EQs with 57.1% by 12/21. Whatever continental or oceanic earthquakes, precursors were both detected in more than 1/2 large events, which may be explained by the radon emanating theory (Pulinets et al., 2006). The radon would emanate from the Earth‟s crust during the earthquake preparation process, and changes the air conductivity and the atmospheric electric field through the formation of large ion clusters over the epicentral area. Maybe the different media of continent and ocean decide the difficulty of radon overflow to atmosphere. According to the focus depth, they were divided into deep EQs (deeper than 70km) and shallow EQs. As shown in Tab. 3, the percent of earthquakes with anomalies before shallow EQs was much higher by 62.0% than that of 45.4% before deep ones. As for the shallow earthquakes, many micro-fractures would be formed near the surface due to accumulation of stress in the seismogenic zone, along which chemical materials such as radon and aerosols would gather, and electromagnetic emissions would propagate easily into the atmosphere and then to the ionosphere, so it can sort of understand that perturbations produced at shallow depth can be much easily detected in ionosphere than those from the deep focus.
Tab.3. Total numbers, abnormal numbers and probability of different types EQs
4.2 The temporal characteristics of plasma anomalies related to earthquakes Based on Tab.2, we summed the occurrence time of each anomaly according to the days before EQs, and if the perturbations for one parameter occurred in approximately same area at the same day by using two methods, it would be considered being only one. From Fig.4, abnormities almost appeared every day from 10 days before EQs to 2 days after EQs, but in 1, 3, 5, 6, 8 days before EQs their 6
occurrence was higher, exceeding median value 11.5, which illustrate that the number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
of anomalies in ionosphere increased in 8 days before EQs, especially in 6, 5 days. Hasbi et al. (2011) investigated the ionospheric variations before four earthquakes with M≥7.9 taking place during 2004-2007 in Sumatra by using GPS and CHAMP data, and their result showed the occurrence of anomalies detected within a few hours to 6 days before the earthquakes. Using GPS TEC data, Liu et al. (2004) found that the seismo-ionospheric precursors were detected 1-5 days prior to 20 major earthquakes in Taiwan. So our results in temporal distribution of plasma anomalies were consistent with others. However, in our research, the biggest number of anomalies occurred just one day after the EQs, not only concentrated before the EQs, which may be related to the occurrence of amount of aftershocks at seismic regions.
Fig.4. Abnormity numbers in each day before EQs
4.3 The spatial distribution feature of plasma perturbations The abnormity numbers in eight directions were summed based on direction column in Tab.2, and if the abnormities appeared in 2 or more directions, each direction would be recorded separately. As shown in Tab.4, for EQs in the geomagnetic north hemisphere, the abnormity numbers were 29 in sum of SE, S, SW, larger than 18 in sum of NW, N, NE directions. For EQs in the geomagnetic south hemisphere, the perturbations were more often located at the north of the epicenters with the sum number of 63 than 32 at their south. The abnormal regions in the ionosphere before EQs were not just above the epicenters, but shifted equatorward with a distance of several degrees to almost twenty degrees. This feature has been demonstrated in other plasma parameters, such as GPS TEC with perturbations occurring at the southeast of the epicenter and its conjugate area at the southern hemisphere on May 9, 3 days before the Wenchuan earthquake in 2008 (Zhao et al., 2008). Tab.4. Abnormal numbers in each direction
Pulinets et al. (2004b) considered this phenomenon was caused by ionospheric particles E×B drift in anomalous electric field penetrating from ground. Kuo et al. (2011) proposed the electrical coupling between ionosphere and surface charges in 7
earthquake fault zone, and they thought the vertical surface electric field drove the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
current in atmosphere and electric field at the bottom of the ionosphere. Whether penetration or secondary electric field in the ionosphere, it moved upward to satellite altitude along the magnetic lines, causing E × B motion, and leading to electron movement to equatorward and also to east and west directions under down and up electric field.
4.4 Comparison of two parameters Besides the same abnormities using different analysis methods, there were 131 records separately on Te or Ne, among which the number of Ne (106) were more than that of Te (25), which illustrate that Ne is much more sensitive to seismic activity than Te. The synchronous abnormities of Ne and Te were only 2 times, including 1 positive correlations and 1 negative correlation. Because of the small synchronous abnormity samples, no statistical regularity can be obtained between Ne and Te before EQs in our study. 4.5 Abnormal characters in shape As shown in Tab. 2, there were 97 positive and 9 negative abnormities in Ne, and for Te, there were 19 positive and 6 negative abnormities respectively. Whatever Ne or Te, positive abnormities were more than negative ones. Liu et al. (2009) found that TEC (total electron content) reduced at southeast on May 6 and increased at southeast on May 9 before Wenchuan earthquake. Yao et al. (2012) also found that both positive and negative anomalies were likely to occur before earthquakes by analyzing GIM TEC before the global M=7.0+ earthquakes in 2010. In other word, electromagnetic environment in the ionosphere has been significantly changed over different EQs or different time of same EQs, so positive and negative abnormities can both appear before EQs, but with our statistics results, positive anomalies may occur more frequently at the altitude of DEMETER satellite of 670 km. 5. Conclusions Based on the analysis of Ne and Te data detected by DEMETER satellite in local nighttime, the ionosphere perturbations before 49 Ms≥7.0 EQs during 2005 to 2010 have been distinguished using moving median and space difference methods within 8
10 days before and 2 days after. Summing up the temporal, spatial distribution 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
characteristics of these anomalies, and their relationship to different type of earthquakes, it can be concluded as follows: 1)
More perturbations in Ne and Te were seen in 1, 3, 5, 6, 8 days before the EQs and 1 day after the EQs.
2)
The ionospheric anomalies always shifted equatorward with several degrees to almost twenty degrees, which may be related to the effect of E×B drift due to the anomalous electric field over the epicentral area.
3)
More disturbances were detected before shallow-focus earthquakes than deep ones. And there was little difference between continental and oceanic ones, both exceeding 1/2 percentage.
4)
Most of the abnormities were positive ones, which demonstrate that Ne increases before EQs at the altitude of 670km of DEMETER.
5)
Perturbations of Ne occurred more often than those of Te, which illustrate that Ne is much more sensitive to seismic activity than Te.
Acknowledgements This work is supported by the National Natural Science Foundation of China (41204109, 41104030) and the National High-Tech Research and Development Program of China (863 Program) (2012AA121004). The authors acknowledge DEMETER satellite center for providing the level 1 data and CENC for providing the down loading earthquake catalogue. .
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Kamogawa, M. Preseismic lithosphere–atmosphere–ionosphere coupling. EOS Transactions. 87 (40), 417-424, 2006. Karia, S., Sarkar, S., Pathak, K. Analysis of GPS-based TEC and electron density by the DEMETER satellite before the Sumatra earthquake on 30 September 2009. International Journal of Remote Sensing. 33(16), 5119-5134, 2012. Kuo, C.L., Huba, J.D., Joyce, G., et al. Ionosphere plasma bubbles and density variations induced by pre-arthquake rock currents and associated surface charges. J. Geophys. Res. 116, A10317, 2011. Le, H., Liu, L., Liu, J.Y., et al. The ionospheric anomalies prior to the M9.0 Tohoku-Oki earthquake. Journal of Asian Earth Sciences. 62, 476-484, 2012. Lebreton, J.P., Stverak, S., Travnicek, P., et al. The ISL Langmuir Probe experiment and its data procession onboard DEMETER: scientific objectives, description and first results. Planetary and Space Science. 54, 472-486, 2006. Li, M., and Parrot M.. Statistical analysis of an ionospheric parameter as a base for earthquake prediction. Journal of Geophysical Research: Space Physics. 118(6), 3731–3739, 2013. Liu, J., Huang, J.P., Zhang, X.M., et al. Anomaly extraction method study and earthquake case analysis based on in-situ plasma parameters of DEMETER satellite. Acta Seismologica Sinica. 35(1), 1-12, 2013. (In Chinese with English abstract) Liu, J.Y., Chen, Y.I., Pulinets, S.A., et al. Seismo-ionospheric signatures prior to M≥6.0 Taiwan earthquakes. Geophysical Research Letters. 27, 3113-3116, 2000. Liu, J.Y., Le, H., Chen, Y.I,, et al. Observations and simulations of seismoionospheric GPS total electron content anomalies before the 12 January 2010 M7 Haiti earthquake. J. Geophys. Res. 116, A04302, 2011. Liu, J. Y., Chuo, Y. J., Shan, S. J., Tsai, Y. B., Chen, Y. I., Pulinets, S. A., and Yu, S. B. Pre-earthquake ionospheric anomalies registered by continuous GPS TEC measurements. Ann. Geophys. 22, 1585–1593, doi:10.5194/angeo-22-1585-2004, 2004. Liu, J.Y., Chen, Y.I., Chen, H.C., et al. Seismoionospheric GPS total electron content anomalies observed before the 12 May 2008 Mw7. 9 Wenchuan earthquake. J. Geophys. Res. 114, A04320, 2009. Parrot, M., Berthelier, J.J., Lebreton J.P., et al. Examples of unusual ionospheric observations made by the DEMETER satellite over seismic regions. Physics and Chemistry of the Earth. 31, 486-495, 2006. Perrone, L., Korsunova, L. P., Mikhailov, A.V. Ionospheric precursors for crustal earthquakes in Italy. Ann. Geophys. 28, 941-950, 2010. Pulinets, S.A., Legen‟ka, A.D., Alekseev, V.A. Pre-earthquakes effects and their possible mechanisms. In: Dusty and Dirty Plasmas, Noise and Chaos in Space and in the Laboratory. New York: Plenum. Publishing. 545-557, 1994 Pulinets, S.A., Legen‟ka, A.D., Gaivoronskaya, T.V., et al. Main Phenomenological features of ionospheric precursors of strong earthquakes. Journal of Atmospheric and Solar–Terrestrial Physics. 65, 1337-1347, 2003. Pulinets, S.A., Liu, J.Y., Safronova, I.A. Interpretation of a statistical analysis of variation in the foF2 critical frequency before earthquake based on data from Chung-Li ionospheric station (Taiwan). Geomagnetism and Aeronomy. 44, 102-106, 2004a. Pulinets,S.A., Boyarchuk, B. Ionospheric precursors of earthquakes. Berlin: Springer-Verlag. 2004b. Pulinets, S.A., Ouzounovet, D., Ciraolo, L., et al. Thermal, atmospheric and ionospheric anomalies around the time of the Colima M7.8 earthquake of 21 January 2003. Ann. Geophys. 24, 835-849, 2006. Sarkar, S., Choudhary, S., Sonakia, A., et al. Ionospheric anomalies associated with the Haiti earthquake of 12 January 2010 observed by DEMETER satellite. Nat. Hazards Earth Syst. Sci. 12, 671-678, 2012. Sharma, K., Das, R.M., Dabas, R., et al. Ionospheric precursors observed at low latitudes around the time of koyna earthquake. Advances in Space Research. 42: 1238-1245, 2008. Xu, T., Hu, Y., Wu, J., et al. Abnormal perturbations in the ionospheric F2 region before Wenchuan earthquake on 12 May 2008. Science China. 53(11), 1671-1674, 2010.Yao, Y. B., Chen, P., Zhang, S., Chen, J. J., Yan, F., and W. F. Peng. Analysis of pre-earthquake ionospheric anomalies before the global M=7.0+ earthquakes in 2010. Nat. Hazards Earth 10
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Syst. Sci. 12, 575-585, 2012. Zeng, Z.C., Zhang, B., Fang, G.Y., et al. The analysis of ionospheric variations before Wenchuan earthquake with DEMETER data. Chinese J. Geophys. 52(1), 11-19, 2009. (In Chinese with English abstract) Zhang, X., Shen, X., Liu, J., et al. Analysis of ionospheric plasma perturbations beforeWenchuan Earthquake. Nat. Hazards Earth Syst. Sci. 9, 1259-1266, 2009. Zhang, X., Shen, X., Liu, J., et al. Ionospheric perturbations of electron density before the Wenchuan Earthquake. International Journal of Remote Sensing. 31(13), 3559-3569, 2010. Zhang, X., Shen, X., Parrot, M., et al. Phenomena of electrostatic perturbations before strong earthquakes (2005-2010) observed on DEMETER. Nat. Hazards Earth Syst. Sci. 12, 75-83, 2012. Zhao, B.Q., Wang, M., Yu, T., et al. Is an unusual large enhancement of ionospheric electron density linked with the 2008 great Wenchuan earthquake? J. Geophys. Res. 113, A11304, 2008.
11
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Table
UT 2005/01/01 06:25 2005/01/19 06:11 2005/02/26 12:56 2005/03/02 10:42 2005/03/20 01:53 2005/03/28 16:09 2005/05/14 05:05 2005/06/13 22:44 2005/06/15 02:50 2005/07/05 01:52 2005/07/24 15:42 2005/08/16 02:46 2005/09/09 07:26 2005/09/26 01:55 2005/11/14 21:38 2006/02/22 22:19 2006/04/20 23:25 2006/05/03 15:26 2006/05/16 10:39 2006/05/16 15:28 2006/05/22 11:11 2006/07/17 08:19 2006/11/15 11:14 2007/01/21 11:27 2007/03/25 00:39 2007/03/25 00:41 2007/04/01 20:39 2007/07/16 10:13 2007/08/01 17:08 2007/09/12 11:10 2007/11/14 15:40 2007/12/09 07:28 2008/01/05 11:01 2008/02/08 09:38 2008/02/20 08:08 2008/03/20 22:32 2008/04/09 12:46 2008/05/02 01:33 2008/05/07 16:45 2008/05/12 06:28 2008/06/13 23:43 2008/07/05 02:12 2008/07/19 02:39 2008/09/08 18:52 2008/09/10 13:08 2008/09/11 00:20 2008/09/29 15:19 2008/10/05 15:52 2008/10/19 05:10 2008/11/16 17:02 2009/01/03 19:43 2009/01/15 17:49 2009/02/11 17:34 2009/02/18 21:53
Tab.1. EQs information table Latitude(°) Longitude(°) Magnitude(Ms) 92.25 141.62 95.62 130.16 130.38 97.05 98.40 -69.11 -126.00 97.23 92.19 141.89 153.79 -76.40 144.53 33.10 167.48 -173.72 -179.30 97.04 166.22 107.40 153.27 126.77 170.31 137.47 157.00 138.91 167.65 101.41 -70.20 -177.50 -130.80 -41.90 95.89 81.54 169.88 -178.11 141.26 103.42 141.29 152.95 141.91 167.01 -38.70 143.78 -177.03 73.67 -173.35 122.45 132.90 154.65 126.68 -175.70
4.72 34.00 2.93 -6.70 33.70 2.03 0.34 -19.41 41.30 1.54 7.83 38.15 -4.38 -5.70 38.33 -20.87 60.97 -19.76 -31.80 -0.10 60.77 -9.30 46.69 0.23 -21.28 37.14 -8.50 37.42 -14.98 -4.90 -22.03 -26.00 51.30 10.70 2.54 35.64 -19.86 52.14 36.24 31.01 38.91 53.83 37.56 -13.03 8.10 41.90 -29.46 39.58 -21.32 1.12 -0.40 47.08 3.40 -26.94
7.1 7.0 7.0 7.0 7.3 8.6 7.0 7.8 7.3 7.2 7.6 7.2 7.0 7.6 7.3 7.6 8.3 7.9 7.5 7.3 7.5 7.4 8.0 7.5 7.2 7.2 7.9 7.0 7.0 8.6 7.9 7.5 7.0 7.3 7.7 7.5 7.2 7.0 7.2 8.2 7.3 7.4 7.2 7.2 7.0 7.3 7.1 7.0 7.0 7.0 7.4 7.3 7.4 7.3
Depth(km) 28 37 33 228 21 34 51 115 10 33 19 30 95 115 11 22 32 54 151 22 17 34 9 22 34 8 10 42 145 25 60 152 10 9 30 21 40 16 31 14 7 636 22 129 10 33 26 27 21 30 23 36 30 18
Type O O O O C O O C O C O O O C O C C O O O C O O O O C O C O O C O O O O C O O O C C O O O O O O C O C C O O O
-174.70 -26.80 -86.20 166.41 -112.90 138.02 92.78 99.60 107.30 -171.57 166.82 157.40 -72.50 128.65 -72.80 100.77 -73.20 -115.30 97.20 96.59 100.96 91.91 136.60 -170.21 150.40 123.86 168.01 141.67
2009/03/19 18:17 2009/04/16 14:57 2009/05/28 08:24 2009/07/15 09:22 2009/08/03 17:59 2009/08/09 10:55 2009/08/10 19:55 2009/08/16 07:38 2009/09/02 07:55 2009/09/29 17:48 2009/10/07 22:03 2010/01/03 22:36 2010/01/12 21:53 2010/02/26 20:31 2010/02/27 06:34 2010/03/05 16:06 2010/03/16 02:21 2010/04/04 22:40 2010/04/06 22:15 2010/04/13 23:49 2010/05/05 16:28 2010/06/12 19:26 2010/06/16 03:16 2010/07/18 05:56 2010/07/18 13:04 2010/07/23 22:51 2010/08/10 05:23 2010/08/13 21:19
-23.00 -60.20 16.70 -45.74 29.00 33.12 14.22 -1.95 -7.80 -14.80 -12.68 -8.80 18.50 25.86 -35.80 -4.37 -36.20 32.10 2.31 33.22 -4.84 7.85 -2.20 52.92 -6.00 5.98 -17.05 12.43
7.7 7.0 7.6 7.7 7.3 7.1 7.7 7.1 7.2 8.1 7.8 7.3 7.7 7.3 8.8 7.2 7.0 7.5 7.9 7.3 7.0 7.6 7.3 7.0 7.2 7.1 7.3 7.0
34 20 10 4 6 299 25 45 49 16 38 25 10 25 35 26 18 10 34 14 27 31 18 10 47 594 30 6
O O O O O O O O O O O O O O C O O C O C O O C O C O O O
Tab.2. Characteristics of abnormities before 49 EQs Nu m
Earthquake information
1 2
2005.2.26(95.62, 2.93) 2005.3.20(130.38, 33.7)
Par am ete r Ne Ne Ne Ne
Amplitu de
Distance
Direction
Time
Characte r
method
Ty pe
- 45% +110% +55%
southeast, northeast southwest southwest southwest
2.23(-3) 3.12(-8) 3.15(-5) 3.16(-4)
decrease increase increase increase
MMM MMM MMM SDM
O C
≥10σ
21° -17° 19.2°-23.5° 23.9°-24.9° 13.4°-15.2°
Ne
≥10σ
7°
southwest
3.20(+10 h)
increase
SDM
Ne
≥ 10σ
13.2°-15.2°
south
3.22(+2)
increase
SDM
23.5°-34.7° 14° 11°
Southwest, northwest east northwest
3.21(-7) 3.22(- 6) 3.22(- 6)
decrease decrease increase
MMM MMM SDM
O
northeast north southeast, northeast east, northeast east
6.30(-5) 7.4(-1) 7.5(+13h) 7.7(+2) 7.7(+2)
increase increase increase increase increase
MMM MMM MMM MMM SDM
C
decrease
SDM
O
decrease increase increase
MMM MMM SDM
O
3
2005.3.28(97.05, 2.03)
Ne Te Ne
-50% -38%
4
2005.7.5(97.23, 1.54)
Ne Ne Ne Ne Ne
+ 120% +45% +140% +120% ≥10σ
18.1° -21.7° 3.7°-13.5° 20° -15.7° 19.5° -23.8° 18°
5
2005.7.24(92.19,7.83)
Ne
≤-10σ
14.3°
northeast
6
2005.9.9（153.79,-4.38）
Te Ne Ne
-30% +250%
33.5° 24.5°-27° 27.8°
northwest northeast northeast
7.24(before a few minutes) 7.25(+1) 8.30(-10) 8.30(-10)
Ne Ne
+70%
5.7°-21° 4°-6°
south, north north
8.30(-10) 8.30(-10)
increase increase
MMM SDM
Ne Ne
+70%
4°-5° 18°
east southeast
9.23(-3) 9.23(-3)
increase increase
MMM SDM
Ne Ne
+70% ≥10σ
18.7°-27.7° 13-22°
northeast southwest
9.24(-2) 9.25(-1)
increase increase
MMM SDM
2005.11.14 (144.53,38.33)
Ne
≤-10σ
18.1°
southwest
11.8(-6)
decrease
MMM
O
+25%
2006.2.22(33.1,-20.87)
Te Ne
11.1°- 24.5° in 2.2°
northwest northeast
11.16(+2) 2.17(-5)
increase increase
MMM SDM
C
7
8 9
2005.9.26(-76.4,-5.7)
≥10σ
≥10σ ≥10σ ≥10σ
≥10σ
C
10
2006.7.17 (107.4,-9.3)
Te Ne Te Ne
+ 30% +80% +35%
11
2007.1.21(26.77,0.23)
+45% +60%
12
2007.3.25(137.47,37.14)
Ne Ne Ne
13
2007.4.1(157,-8.5)
+70% +50%
14
2007.7.16(138.91,37.42)
Ne Ne Ne
15
2007.8.1(167.65,-14.98)
Ne Ne
+150%
Ne Ne
+50%
Ne Ne Ne Te Ne
+120% +120% +120% +30%
Ne Ne
+ 45%
16
2007.9.12(101.41,-4.9)
17
2007.11.14(-70.2,-22.03)
18
2007.12.9(-177.5,-26)
19
2008.5.2(-178.11,52.14)
20
2008.7.19(141.91,37.56)
21
2008.9.8 (167.01,-13.03)
12°-14.2° 29.3°-30.3° 17.6°-25.1° 19.3°
southeast southeast southeast southwest
7.13(-4) 7.15(-2) 7.16(-1) 7.17(+8 h)
increase increase increase increase
MMM MMM MMM SDM
O
20.6°-21.5° 19.3°-25.7° 27.7°
southeast southeast southeast
1.11(-10) 1.21(+1) 3.20(-5)
increase increase increase
MMM MMM SDM
O
9.7°to 17.4° 17.3°- 24.9° 17.8°, 21.3°-24.4° 13.9°-20.8° 20°
northeast northwest southeast
3.29(-3) 3.29(-3) 7.7(-9)
increase increase increase
MMM MMM SDM
O
northeast northeast
7.24(-8) 7.24(-8)
increase increase
MMM SDM
O
16° 14°
northeast northeast
9.8(-4) 9.8(-4)
increase increase
MMM SDM
O
12.9°-21.3° 22.2°-25.9° 21.3° -26.4° 15.9° -20.5° 27.8°
southeast, northeast northeast northeast southwest northwest
11.13(-1) 11.15(+1) 11.29(-10) 11.30(-9) 12.1(-8)
increase increase increase increase increase
MMM MMM MMM MMM SDM
C
≥10σ
20.7° -24.1° 18.1° -18.4°
northwest west
12.3(-6) 12.4(-5)
increase increase
MMM SDM
Ne
≥10σ
26.6°
southwest
12.5(-4)
increase
SDM
Ne
≥10σ
24.4° -26.1°
southwest
12.8(-1)
increase
SDM
Ne
≥10σ
26.2°
northwest
4.22(-10)
increase
SDM
Te Te Te
+26% +18%
17.6° -17.8° 21.1° -25.8° 26.2°
northeast northwest northwest
4.25(-7) 4.25(-7) 4.25(-7)
increase increase increase
MMM MMM SDM
Te Te Ne Ne
+25% +30% +145%
12.5° -15.1° 21.9° -22.7° 21° -26.4° 16.6°
northwest northeast northeast northeast
7.15(-4) 7.17(-2) 8.30(-9) 8.31(-8)
increase increase increase increase
MMM MMM MMM SDM
Ne Ne
+ 60% ≥10σ
23.1° -24.4° 6.3° -18.1°
northeast north
9.2(-6) 9.2(-6)
increase increase
MMM SDM
Ne
≥10σ
22°, 12.8° -15.6°
northeast, northwest
9.3(-5)
increase
SDM
Ne Ne
+100% ≥10σ
19.4° -20.3° 17.2° -24.4°
northeast northwest
9.9(+1) 9.10(+2)
increase increase
MMM SDM
≥10σ
≥10σ
≥10σ ≥10σ ≥10σ
≥10σ
≥10σ
≥10σ
C
C
O
O
O O
22
2008.9.10(-38.7,8.1)
Ne
≥10σ
25.6°
southwest
9.10(-11h)
increase
SDM
O
23 24
2008.9.29(-177.03,-29.46) 2008.10.5(73.67,39.58)
Ne Ne Ne
+70% +80%
20° -21.5° 17.1° -22.5° 17.2° -20.6°
northeast southeast southeast
9.21(-8) 9.25(-10) 9.25(-10)
increase increase increase
MMM MMM SDM
O C
Ne Ne
+75% ≥10σ
28.3° -32.4° 16.1° -20.1°
southeast south
10.6(+1) 10.6(+1)
increase increase
MMM SDM
Ne
≥10σ
18.7°
southeast
10.16(-3)
increase
SDM
O
26
2008.10.19(-173.35,-21.32 ) 2008.11.16 (122.45,1.12)
Ne
≥10σ
19°-20.6°
southwest
11.14(-2)
increase
SDM
C
27
2009.2.11(126.68,3.4)
Ne
≥10σ
17°
north
2.6(-5)
increase
SDM
O
28
2009.2.18(-175.7,-26.94)
Ne
≥10σ
25.1°-28.4°
southwest
2.10(-8)
increase
SDM
O
Te
≤-10σ
25.1°-28.4°
southwest
2.10(-8)
decrease
SDM
Ne Te Ne Te Ne Ne Ne Te Te Te Te Ne
+80% +35% +60% +28% +65% +60% +80% +28% +25% +25% +30%
northeast southwest north southwest north northeast southeast, northeast northwest northwest northwest northeast south
2.11(-7) 2.11(-7) 2.13(-5) 2.13(-5) 2.16(-2) 3.16(-3) 5.19(-9) 5.23(-5) 5.26(-2) 7.27(-7) 7.31(-2) 8.5(+2)
increase increase increase increase increase increase increase increase increase increase increase increase
MMM MMM MMM MMM MMM MMM MMM MMM MMM MMM MMM SDM
O O
25
≥10σ
29 30
2009.3.19(-174.7,-23.0) 2009.5.28(-86.2,16.7)
31
2009.8.3(-112.9,29)
≥10σ
17.8°-23.4° 8.7°-13.7° 16.5°-20.2° 22.4°-23.4° 5.9°-9.2° 11° 24.8°-20.6° 17.5°-24.4° 19.7°-23.3° 16.1°-17.7° 13.1°-18.8° 13°
32
2009.8.10(92.78,14.22)
Ne
≥10σ
11.7°-17.1°
northwest
7.31(-10)
increase
SDM
O
33
2009.8.16 (99.6,-1.95)
Ne
≤10σ
17.8°
southwest
8.8(-8)
decrease
SDM
O
Ne
≥10σ
18.4°-15.2°
southeast, northeast
8.10(-6)
increase
SDM
Ne
≥10σ
19°-21.6°
northeast
8.16(+6h)
increase
SDM
Ne
≥10σ
9°
north
8.24(-9)
increase
SDM
Ne Ne
+100% ≥10σ
12.9°-21.9° 12.8°-14.5°
northeast northeast
8.29(-4) 8.29(-4)
increase increase
MMM SDM
Ne
≥10σ
2.2°
northwest
9.3(+1)
increase
SDM
34
2009.9.2 (107.3,-7.8)
O
O
35
2009.9.29 (-171.57,-14.8)
36
2009.10.7 (166.82,-12.68)
37
2010.1.3(157.4,-8.8)
38
2010.1.12(-72.5,18.5)
39
2010.2.26(128.65,25.86)
40
2010.2.27(-72.8,35.8)
41
2010.3.5(100.77,-4.37)
Ne Ne
+120%
Ne
≥10σ
Ne
≥10σ
Ne Ne Ne Ne
+160% +70% +170% +58%, +60% -27% +145%
≥10σ
Te Ne Ne
≥10σ
Te Te Ne Ne
-26% +28% +95%
Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne
+60% +70% -45% +40% +100% +90% -43% +37% +35% +110% +55% +130% +25% +70%
≥10σ
≥10σ
7.4°-20.2° 6.7°-9.2°
northeast northeast
9.24(-5) 9.24(-5)
increase increase
MMM SDM
O
18.2°-19.2°,12.2° -14.9° 18.0°-19.3°
northeast, northwest
9.26(-3)
increase
SDM
northeast
9.29 (-10h)
increase
SDM
10.8°-20.3° 19.2° 19.6°-24.9° 17.9° and 11.6°
northeast northeast southeast, northeast southeast
9.30(-7) 10.2(-5) 10.5(-2)
MMM MMM MMM MMM
O
1.3（-12h）
increase increase increase increase
26.8°- 31.3° 26.1°- 33.4° 10.2°- 11.7°
northwest southeast southwest
1.2(-10) 1.3(-9) 1.4(-8)
decrease increase increase
MMM MMM SDM
O
24.2°- 25.4° 18.1° 15.4°- 21.4° 13.4°- 17.1°
northeast northeast southeast southeast
1.6(-6) 1.11(-1) 1.12(-19h) 1.12(-19h)
decrease increase increase increase
MMM MMM MMM SDM
27.4°- 31.9° 20.1°-3.4° 23.8° -27.2° 19°-24.8° 12.2°-20° 14.3°-19.4° 12.7°-15.1° 4.9° 30° 22.6° -25.4° 17.8°
southeast southeast, northwest southeast southwest southeast southwest northeast northwest northwest southeast, northeast northwest
1.13(+1) 2.19(-7) 2.20(-6) 2.21(-5) 2.27(+1) 2.27(+1) 2.24(-3) 2.26(-1) 2.26(-1) 2.27(-6) 3.3(-2)
increase increase decrease increase increase increase decrease increase increase increase increase
MMM MMM MMM MMM MMM MMM MMM MMM MMM MMM SDM
southeast, northeast northwest southeast northeast northeast
3.6(+1) 3.8(-8) 3.17(+1) 3.18(+2) 3.31(-6)
increase increase increase increase decrease
MMM MMM MMM MMM SDM
O
O
C
O
42
2010.3.16(-73.2,-36.2)
43
2010.4.6(97.2,2.31)
Ne Ne Te Ne Te
≤10σ
16.6° to 15.9° 15.7° -22.8° 30.8°-37.5° 19.7° -23.1° 3.6°
44
2010.5.5(100.96,-4.84)
Ne
≤10σ
20.5°
northeast
4.27(-8)
decrease
SDM
O
2010.6.16(136.6,-2.2)
Ne Ne Ne
+50% +70%
18.9°-24.1° 11.2° to 23° 6.7°
northeast northwest southwest
4.30(-5) 6.13(-3) 6.13(-3)
increase increase increase
MMM MMM SDM
C
Te Te Ne
+20% +28%
15.5°-16.5° 22.7° -23.1° 6.7°
east southeast southeast
7.10(-8) 7.16(-2) 7.12(-6)
increase increase decrease
MMM MMM SDM
Te Ne Ne
+30% +100%
25.8° -27.7° 16.5° -21.9° 16.2°
southwest northwest northwest
7.16(-2) 7.31(-10) 7.31(-10)
increase increase increase
MMM MMM SDM
Ne Ne Ne
+70% +70%
17.2° -23.2° 20.2° -23.7° 21.3° -24.4°
northeast northwest northwest
8.7(-3) 8.7(-3) 8.7(-3)
increase increase increase
MMM MMM SDM
Ne Ne
+150%
24.7° -24.2° 18.0°
southeast, northeast southeast
8.10(+4h) 8.12(+2)
increase increase
MMM SDM
Ne Ne Ne
+100% +100%
increase increase increase
MMM MMM SDM
≥10σ
southeast southwest, northwest east, southwest, northwest southwest
8.7(-6) 8.7(-6) 8.7(-6)
Ne
15.9°-18.6° 17.5° -16.4° 10°-10.8°,15.2°14.6° 14.3°
8.14(+1)
increase
SDM
45 46
2010.7.18(-170.21,52.92)
47
2010.7.18(150.4,-6)
48
49
2010.8.10(168.01,-17.05)
2010.8.13(141.67,12.43)
≥10σ
≤10σ
≥10σ
≥10σ ≥10σ
≥10σ
O
O
O C O
O
Annotation: Distance of SDM was calculated from epicenter to abnormal grid center; Distance of MMM was calculated from epicenter to start and end abnormal spots, and amplitude indicated the difference between observation data and threshold for the peak in this orbit.
Tab.3. Total numbers, abnormal numbers and probability of different types EQs Type Numbers Earthquake numbers Abnormal numbers Percentage
Continental EQs
Oceanic EQs
Deep EQs
Shallow EQs
21 12
61 37
11 5
71 44
57.1％
60.7％
45.4％
62.0％
Tab.4. Abnormal numbers in each direction
Direction Numbers Magnetic north EQs Magnetic south EQs
E
SE
S
SW
W
NW
N
NE
2 2
14 19
3 1
12 12
0 1
10 18
0 7
8 38