- Email: [email protected]
Geophysical observations during the flight of the Chelyabinsk meteoroid
Available online at www.sciencedirect.com
ScienceDirect Russian Geology and Geophysics 55 (2014) 405–410 www.elsevier.com/locate/rgg
Geophysical observations during the flight of the Chelyabinsk meteoroid V.S. Seleznev *, A.V. Liseikin, A.A. Emanov, A.Yu. Belinskaya Geophysical Survey, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia Received 5 August 2013; accepted 11 October 2013
Abstract The paper describes the effects of the passage of the Chelyabinsk meteoroid (which exploded on 15 February 2013 over the Chelyabinsk Region), which were established from geophysical data from West Siberian stations. The trajectory and speed of the meteoric body from the start of the glow to the breakup were recorded by surveillance cameras and dashcams. Records from broadband seismic stations were used to determine the exact time of the explosion (03:20:34 UTC) from the arrival times of the surface wave produced by this event. The explosion energy was estimated from the surface-wave amplitudes at ~100 kilotons on the assumption that the wave originated from a point source similar to a high-altitude thermonuclear explosion. A database of records from seismic stations obtained during the meteoroid passage has been compiled. Keywords: Chelyabinsk meteoroid; meteoroid trajectory; surface waves; energy of high-altitude explosion
Introduction
Calculated trajectory and speed of the bolide
An extraordinary event occurred on 15 February 2013. The meteoroid which passed over Siberia and exploded in the Chelyabinsk Region attracted great attention worldwide for two reasons: (1) very seldom does a meteoric body explode near a large populated place; (2) records of the bolide by many surveillance cameras, dashcams, and cell phone cameras spread quickly around the globe. The main reason why the meteoroid attracted our attention was that its path ran close to the Klyuchi observatory (Novosibirsk Region), which is the largest in Siberia. The parameters of the ionosphere, magnetic field, and cosmic rays undergo regular monitoring here. Also, the area is covered with the seismic-station network of the Geophysical Survey SB RAS, deployed in the Altai–Sayan and Baikal regions. This well-developed network for geophysical-field observations permitted researchers to record the effects of the meteoroid passage. The paper describes the effects of the flight of the Chelyabinsk meteoroid and its explosion, which were established from the geophysical data from West Siberian stations.
The vast collection of video records from different observation sites permits very accurate determinations of the trajectory and speed of the bolide from the position of the visible trail on the images and the sounds at the site of its explosion (Table 1). Our calculations were based on the time difference between the observed effects (light flashes, acoustic effects, and shock wave) during the bolide passage. This is because the time in the videos was mostly not synchronized with the UTC, thus making it difficult to determine the exact moments of the events. First, we located the ground projection of the point at which the meteoroid began to glow on entering the atmosphere. This point was determined from the records obtained in Tyumen’, Orenburg, Alga, Shadrinsk, Miass, Chelyabinsk, and Kurgan (Table 1). They were used to calculate the direction toward the bolide at the moment of its appearance in the videos. According to our calculations, the meteoroid started to glow at point T3 (Fig. 1) at an altitude of 68 km (estimated from the angle of the point at which the bolide started to glow with respect to the horizon in the video from Kurgan). The coordinates were determined from the intersection of straight lines drawn from the observation sites toward the point at which the meteoroid started to glow, with atmospheric refraction neglected. The projection of point T2 (Fig. 1), at which the meteoroid began to explode, was located from the intersection of two straight lines drawn from Revolution Square and the market
* Corresponding author. E-mail address: [email protected] (V.S. Seleznev)
1068-7971/$ - see front matter D 201 4, V.S. So bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.201 + 4.01.022
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V.S. Seleznev et al. / Russian Geology and Geophysics 55 (2014) 405–410
Table 1. Videos used to determine the flight parameters of the Chelyabinsk meteoroid Site
N
E
Links
Notes
deg. T1
54.838807
61.005291
–
Termination of glow
T2
54.853240
61.521180
–
Start of explosions
T3
54.884089
65.654046
–
Start of glow
H = 26.5
54.843837
61.400503
–
Altitude determination
Kurgan
55.442143
65.335400
http://www.youtube.com/watch?v=FAMcMmzIugU
Flight
Shadrinsk
56.108054
63.657312
http://www.youtube.com/watch?v=MvEYTwwzB0U
Flight
Tyumen’
57.146084
65.583344
http://www.youtube.com/watch?v=nFtcfy9kdrM
Flight
Alga
49.920020
57.334851
http://www.youtube.com/watch?v=EE_LampPEQg
Flight
Market in Korkino
54.890935
61.399572
http://www.youtube.com/watch?v=yfEaUT2yr–A
Flight
Revolution Square, Chelyabinsk
55.160187
61.402664
http://www.youtube.com/watch?v=JvEqPjEUNcMhttp:// Partly recorded flight, www.youtube.com/watch?v=JvEqPjEUNcM exact time in the video
A car near an office, Chelyabinsk
55.150049
61.363366
http://www.youtube.com/watch?v=gQ6Pa5Pv_io
–
South Ural State University, building 3b, Chelyabinsk
55.158864
61.364974
http://directpress.ru/v–rossii/15079–chelyabinskij– meteorit–video–s–kamer–nablyudeniya–yuurgu–15– fevralya–2013–goda
Sound
Orenburg
51.712416
55.206248
http://infonavigator.biz/ru/groups/139/news–332.html
Flight
Al’met’evsk
54.901363
52.249589
http://www.youtube.com/watch?v=qUOMj1Uc1q8
–
Kopeisk
55.097365
61.608469
http://www.youtube.com/watch?v=0L0–Irkj7–c
Wind blowing toward Chelyabinsk, explosion time estimation
Roza Village, Chelyabinsk Region
54.905852
61.457576
http://www.youtube.com/watch?v=iMVWECEMKP4
Explosion time estimation
Kostanay
53.225473
63.640199
http://www.youtube.com/watch?v=RCGUdj8cQ9s
–
Miass
54.944242
60.055896
http://www.youtube.com/watch?v=GtBqypYKPrw
–
Pervomaiskii Village
54.872644
61.200792
http://www.youtube.com/watch?v=R99zvcrqXo8
Explosion time estimation
Victory Avenue, Chelyabinsk
55.188575
61.360038
http://www.youtube.com/watch?v=mOf1oUg7BF4
Exact time in the video, sound heard 152 s later
in the direction of maximum glow. The latter was determined during frame-by-frame viewing of the videos for these sites (Table 1). The moment of the last flash (T1) was recorded by a surveillance camera in Revolution Square. The straight line drawn in this direction and intersecting with the flight trajectory, together with the lamp-post shadow in the square, permit determining the projection coordinates and height (21 km). Fourteen seconds passed from the start of the glow to the last flash. The meteoric body moved with a speed of ~15 km/s from T2 to T1 (33.7 km along the trajectory, time 2.2 s) and with a speed of ~22 km/s from T3 to T2 (262 km, time 11.8 s). Therefore, when the meteoroid committed entry, its speed was no less than 30 km/s. A photograph (Fig. 1) taken with the MET-7 satellite shows a condensation trail from the meteoroid passage through the atmosphere (http://g1.s3.forblabla.com/u34/photoECA8/20973 644132-0/original.jpeg#20973644132). The bolide moved at 7°–9° to the Earth’s surface, so that the projection of its trajectory at this site is parallel to latitude 55. On the assumption that the meteoroid had a straight trajectory before its breakup, our calculations show that it passed 140 km south of Novosibirsk, at an altitude of ~300 km. Also, this is confirmed by variation in the ionospheric parameters over Novosibirsk. The meteoric body left an ionized trail at
altitudes of 100 km or less, which was up to several tens of kilometers long and had an initial diameter of several meters. The trail was observed for fractions of a second to several minutes. On 15 February 2013, all the ionospheric characteristics over Novosibirsk were close to the month averages and showed no disturbances (Fig. 2).
Acoustic waves We are particularly interested in the path segment T1–T2, because the bolide and/or its fragments exploded several times in this area. This is evident from acoustic waves recorded at several sites. Discrete explosions took place at the beginning and end of the segment between T1 and T2. Time–distance curves for the acoustic wave at different altitudes of the explosion site are shown in Fig. 3 together with the direction of its rays. It is evident that the shadow zone appeared at distances of 60 km (altitude 25 km) and ~75 km (altitude 30 km). The sound reached Korkino 88 s later (with a speed 0.31 km/s, this corresponds to 27.3 km). In Pervomaiskii Village, the sound was recorded ~40 s later. This implies that the first sound wave traveled for ~75 s from an altitude of 23 km and for ~115 s from T2. In Chelyabinsk,
V.S. Seleznev et al. / Russian Geology and Geophysics 55 (2014) 405–410
407
Fig. 1. Projection of the meteoroid trajectory with located elements. 1, position of surveillance cameras; 2, trajectory points, located using video records; 3, trajectory.
the acoustic wave was recorded 120–150 s later. As the velocity of sound waves is higher near the Earth’s surface than at some altitude and the wind near the surface was blowing from the explosion site to the city, the horizontal component of velocity was considerably higher in Chelyabinsk than in the villages near the meteoroid trajectory. Hence the large number of broken windows in Chelyabinsk. Precise calculations require known wind velocity at different altitudes and its direction. Unfortunately, we do not have these data at our disposal, but they can be obtained if we analyze the image of smoke from the chimneys. Eyewitnesses in Miass (60–65 km from the explosion epicenter) deny having heard the sound. This is explained by the facts that the shadow zone of the sound wave from the source at an altitude of 21 km began at a distance of 60 km from the epicenter (Fig. 3) and that the wind was blowing from Miass to Chelyabinsk. The radius of the area in which the sound of the explosion could be heard is estimated at 90 km from T2. From T3 (altitude of glow 68 km), the bolide could be seen in an area up to 800 km east of T3 and ~1000 km west. The set of sound waves from this path segment formed the sound wave which was recorded worldwide (http://www.iris. edu/dms/nodes/dmc/specialevents/2013/02/19/chelyabinsk-ru s-sia-bolide-meteor/#sthash.7NCko4fy.dpuf).
Seismic effects The meteoroid fragments showered down on an area no less than 20 km in size latitudinally and 40 km longitudinally. Only the waves resulting from the fall of the sound wave to the Earth’s surface were recorded at the Arti (ARU) and
Fig. 2. Critical frequencies of ionospheric layers E, F1, and F2 the day before and during the meteoroid passage. 1, moment of the meteoroid passage; 2, 3, data for 14 and 15 February 2013, respectively; 4, month average critical frequencies of layer F2 with a standard deviation.
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Fig. 3. Calculation of the propagation parameters of acoustic waves from the meteoroid explosion in the atmosphere. a, Speed of sound vs. altitude; b, time–distance curves for the acoustic waves at different altitudes of the source; c, ray trajectories at source altitudes of 25 and 30 km. 1, values after (State Standard 44-01, 1981); 2, interpolated values; 3, source altitude (km).
Sverdlovsk (SVE) seismic stations, whereas earlier times did not permit reliable determination of the arrivals of any waves. We can only give a rough estimate of the maximum possible seismic energy of the earthquake caused by the fall of the meteoroid fragments. The application of approaches used in seismology to determine the energy of earthquake foci showed that the maximum possible energy of the earthquake did not exceed class 9 (otherwise, the seismic-wave arrivals would be conspicuous against the background of the microseisms on seismograms).
Unique records are available from the seismic stations of IRIS GSN/University of California San Diego, the CentralAsian Real-Time Earthquake Monitoring Network, GFZ Potsdam, the Kazakhstan National Data Center, the Geophysical Survey RAS, and the Geophysical Survey SB RAS (Fig. 4). Waves of this type are produced by atmospheric nuclear and thermonuclear explosions (Kogan, 1975). However, these are point sources, whereas the source in the case of the Chelyabinsk meteoroid extended for 33.7 km.
V.S. Seleznev et al. / Russian Geology and Geophysics 55 (2014) 405–410
409
Fig. 4. Arrangement of broadband seismic stations (a) and seismograms with a record of a vertical surface wave (b). 1, epicenter of the meteoroid explosion; 2, seismic stations. t, Time; L, epicentral distance (km); v, reduction rate (3.15 km/s); v*, apparent velocity of the surface wave; ∆, epicentral distance.
The explosion energy was estimated from the surface-wave amplitude by the technique described in (Kogan, 1975). In accordance with this technique, we used a theoretical dependence between the dimensionless energy of the Rayleigh wave and the explosion energy in the case of a high-altitude (30 km) source (Fig. 5). Data from five broadband stations were used to calculate the Rayleigh-wave energy (ER) and the nondimensionalizing parameter F. The figure shows that the explosion energy is 70 to 140 kilotons at different stations, the average value being ~100 kilotons. We emphasize that this estimate presupposes a point source. The reconstruction of the seismic picture requires an accurate time correlation of the events accompanying the meteoroid passage. The timing accuracy on the seismic records is usually higher than 1 ms. The time on the dashcams was taken almost arbitrarily, except the records from the surveillance cameras in Revolution Square and Victory Avenue. If our determination of the meteoroid trajectory is correct, the
distance from the center of segment T1–T2 (lake near Shumakovo Village) to the surveillance cameras is 24 km and the arrival time of the sound wave is 77 s. The time in the source, calculated from the surface-wave arrivals at the closest stations, is 3:21:51 UTC (Fig. 4). Consequently, the explosion took place at 03:20:34 UTC, according to the seismic data. The meteoroid became visible in the atmosphere at 3:20:20 UTC (because 14 s passed from the start of the glow to the explosion). This suggests that the clocks on the surveillance cameras in Revolution Square and Victory Avenue showed correct time and our calculations are accurate.
Conclusions Waves of unusual nature are observed on the seismograms, but the number of the stations is too small to carry out their reliable correlation or to find out their physical origin. Most
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V.S. Seleznev et al. / Russian Geology and Geophysics 55 (2014) 405–410
Also, the excitation of waves by the meteoric body is an important issue: It might have excited both acoustic and ion plasma waves. However, waves of all these types attenuate very strongly when the wavelength is close to, or shorter than, the free path. Therefore, these waves have no significant effect on the processes going on near the body (Al’pert et al., 1963). Nevertheless, the passage of the Chelyabinsk meteoroid might have created conditions for the propagation of such waves toward the Earth, which yielded the unusual waves on the seismograms. Modeling of the process might provide a clue to many problems that arose during the primary processing of the data. Data obtained during such events should be stored for subsequent detailed analysis. As the seismic data from the Geophysical Survey SB RAS might not be available to all researchers, we compiled a database (ftp://ftp.gs.sbras.ru/pub/ meteor/). In addition, it contains freeze frames with drawings used to determine the meteoroid trajectory. The authors thank A.G. Yakovlev for help with the plotting of the time-distance curves for the sound waves at different source altitudes. Fig. 5. To the determination of the energy (Q) of the meteoroid explosion using the dependence on the dimensionless energy (ER/F) of a surface wave, after (Kogan, 1975).
likely, the meteoric body moved in the sky over Novosibirsk with supersonic speed through a strongly rarefied medium (the traveltime path of the particles is long compared to its size). Ordinary methods of hydrodynamics or aerodynamics cannot be used to describe the effects in the vicinity of the body in such a rarefied medium, so that the kinetic theory is required.
References Al’pert, Ya.L., Gurevich, A.V., Pitaevskii, L.P., 1963. Effects induced by fast-moving artificial satellite in ionosphere or interplanetary media. Uspekhi Fizicheskikh Nauk 79 (1), 23–80. Kogan, S.Ya., 1975. Seismic Energy and Methods for Its Determination [in Russian]. Nauka, Moscow. State Standard 44-01, 1981. Standard Atmosphere. Parameters. Introduction 01.07.82 [in Russian]. Izd. Standartov, Moscow.
Editorial responsibility: M.I. Epov
ScienceDirect Russian Geology and Geophysics 55 (2014) 405–410 www.elsevier.com/locate/rgg
Geophysical observations during the flight of the Chelyabinsk meteoroid V.S. Seleznev *, A.V. Liseikin, A.A. Emanov, A.Yu. Belinskaya Geophysical Survey, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia Received 5 August 2013; accepted 11 October 2013
Abstract The paper describes the effects of the passage of the Chelyabinsk meteoroid (which exploded on 15 February 2013 over the Chelyabinsk Region), which were established from geophysical data from West Siberian stations. The trajectory and speed of the meteoric body from the start of the glow to the breakup were recorded by surveillance cameras and dashcams. Records from broadband seismic stations were used to determine the exact time of the explosion (03:20:34 UTC) from the arrival times of the surface wave produced by this event. The explosion energy was estimated from the surface-wave amplitudes at ~100 kilotons on the assumption that the wave originated from a point source similar to a high-altitude thermonuclear explosion. A database of records from seismic stations obtained during the meteoroid passage has been compiled. Keywords: Chelyabinsk meteoroid; meteoroid trajectory; surface waves; energy of high-altitude explosion
Introduction
Calculated trajectory and speed of the bolide
An extraordinary event occurred on 15 February 2013. The meteoroid which passed over Siberia and exploded in the Chelyabinsk Region attracted great attention worldwide for two reasons: (1) very seldom does a meteoric body explode near a large populated place; (2) records of the bolide by many surveillance cameras, dashcams, and cell phone cameras spread quickly around the globe. The main reason why the meteoroid attracted our attention was that its path ran close to the Klyuchi observatory (Novosibirsk Region), which is the largest in Siberia. The parameters of the ionosphere, magnetic field, and cosmic rays undergo regular monitoring here. Also, the area is covered with the seismic-station network of the Geophysical Survey SB RAS, deployed in the Altai–Sayan and Baikal regions. This well-developed network for geophysical-field observations permitted researchers to record the effects of the meteoroid passage. The paper describes the effects of the flight of the Chelyabinsk meteoroid and its explosion, which were established from the geophysical data from West Siberian stations.
The vast collection of video records from different observation sites permits very accurate determinations of the trajectory and speed of the bolide from the position of the visible trail on the images and the sounds at the site of its explosion (Table 1). Our calculations were based on the time difference between the observed effects (light flashes, acoustic effects, and shock wave) during the bolide passage. This is because the time in the videos was mostly not synchronized with the UTC, thus making it difficult to determine the exact moments of the events. First, we located the ground projection of the point at which the meteoroid began to glow on entering the atmosphere. This point was determined from the records obtained in Tyumen’, Orenburg, Alga, Shadrinsk, Miass, Chelyabinsk, and Kurgan (Table 1). They were used to calculate the direction toward the bolide at the moment of its appearance in the videos. According to our calculations, the meteoroid started to glow at point T3 (Fig. 1) at an altitude of 68 km (estimated from the angle of the point at which the bolide started to glow with respect to the horizon in the video from Kurgan). The coordinates were determined from the intersection of straight lines drawn from the observation sites toward the point at which the meteoroid started to glow, with atmospheric refraction neglected. The projection of point T2 (Fig. 1), at which the meteoroid began to explode, was located from the intersection of two straight lines drawn from Revolution Square and the market
* Corresponding author. E-mail address: [email protected] (V.S. Seleznev)
1068-7971/$ - see front matter D 201 4, V.S. So bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.201 + 4.01.022
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V.S. Seleznev et al. / Russian Geology and Geophysics 55 (2014) 405–410
Table 1. Videos used to determine the flight parameters of the Chelyabinsk meteoroid Site
N
E
Links
Notes
deg. T1
54.838807
61.005291
–
Termination of glow
T2
54.853240
61.521180
–
Start of explosions
T3
54.884089
65.654046
–
Start of glow
H = 26.5
54.843837
61.400503
–
Altitude determination
Kurgan
55.442143
65.335400
http://www.youtube.com/watch?v=FAMcMmzIugU
Flight
Shadrinsk
56.108054
63.657312
http://www.youtube.com/watch?v=MvEYTwwzB0U
Flight
Tyumen’
57.146084
65.583344
http://www.youtube.com/watch?v=nFtcfy9kdrM
Flight
Alga
49.920020
57.334851
http://www.youtube.com/watch?v=EE_LampPEQg
Flight
Market in Korkino
54.890935
61.399572
http://www.youtube.com/watch?v=yfEaUT2yr–A
Flight
Revolution Square, Chelyabinsk
55.160187
61.402664
http://www.youtube.com/watch?v=JvEqPjEUNcMhttp:// Partly recorded flight, www.youtube.com/watch?v=JvEqPjEUNcM exact time in the video
A car near an office, Chelyabinsk
55.150049
61.363366
http://www.youtube.com/watch?v=gQ6Pa5Pv_io
–
South Ural State University, building 3b, Chelyabinsk
55.158864
61.364974
http://directpress.ru/v–rossii/15079–chelyabinskij– meteorit–video–s–kamer–nablyudeniya–yuurgu–15– fevralya–2013–goda
Sound
Orenburg
51.712416
55.206248
http://infonavigator.biz/ru/groups/139/news–332.html
Flight
Al’met’evsk
54.901363
52.249589
http://www.youtube.com/watch?v=qUOMj1Uc1q8
–
Kopeisk
55.097365
61.608469
http://www.youtube.com/watch?v=0L0–Irkj7–c
Wind blowing toward Chelyabinsk, explosion time estimation
Roza Village, Chelyabinsk Region
54.905852
61.457576
http://www.youtube.com/watch?v=iMVWECEMKP4
Explosion time estimation
Kostanay
53.225473
63.640199
http://www.youtube.com/watch?v=RCGUdj8cQ9s
–
Miass
54.944242
60.055896
http://www.youtube.com/watch?v=GtBqypYKPrw
–
Pervomaiskii Village
54.872644
61.200792
http://www.youtube.com/watch?v=R99zvcrqXo8
Explosion time estimation
Victory Avenue, Chelyabinsk
55.188575
61.360038
http://www.youtube.com/watch?v=mOf1oUg7BF4
Exact time in the video, sound heard 152 s later
in the direction of maximum glow. The latter was determined during frame-by-frame viewing of the videos for these sites (Table 1). The moment of the last flash (T1) was recorded by a surveillance camera in Revolution Square. The straight line drawn in this direction and intersecting with the flight trajectory, together with the lamp-post shadow in the square, permit determining the projection coordinates and height (21 km). Fourteen seconds passed from the start of the glow to the last flash. The meteoric body moved with a speed of ~15 km/s from T2 to T1 (33.7 km along the trajectory, time 2.2 s) and with a speed of ~22 km/s from T3 to T2 (262 km, time 11.8 s). Therefore, when the meteoroid committed entry, its speed was no less than 30 km/s. A photograph (Fig. 1) taken with the MET-7 satellite shows a condensation trail from the meteoroid passage through the atmosphere (http://g1.s3.forblabla.com/u34/photoECA8/20973 644132-0/original.jpeg#20973644132). The bolide moved at 7°–9° to the Earth’s surface, so that the projection of its trajectory at this site is parallel to latitude 55. On the assumption that the meteoroid had a straight trajectory before its breakup, our calculations show that it passed 140 km south of Novosibirsk, at an altitude of ~300 km. Also, this is confirmed by variation in the ionospheric parameters over Novosibirsk. The meteoric body left an ionized trail at
altitudes of 100 km or less, which was up to several tens of kilometers long and had an initial diameter of several meters. The trail was observed for fractions of a second to several minutes. On 15 February 2013, all the ionospheric characteristics over Novosibirsk were close to the month averages and showed no disturbances (Fig. 2).
Acoustic waves We are particularly interested in the path segment T1–T2, because the bolide and/or its fragments exploded several times in this area. This is evident from acoustic waves recorded at several sites. Discrete explosions took place at the beginning and end of the segment between T1 and T2. Time–distance curves for the acoustic wave at different altitudes of the explosion site are shown in Fig. 3 together with the direction of its rays. It is evident that the shadow zone appeared at distances of 60 km (altitude 25 km) and ~75 km (altitude 30 km). The sound reached Korkino 88 s later (with a speed 0.31 km/s, this corresponds to 27.3 km). In Pervomaiskii Village, the sound was recorded ~40 s later. This implies that the first sound wave traveled for ~75 s from an altitude of 23 km and for ~115 s from T2. In Chelyabinsk,
V.S. Seleznev et al. / Russian Geology and Geophysics 55 (2014) 405–410
407
Fig. 1. Projection of the meteoroid trajectory with located elements. 1, position of surveillance cameras; 2, trajectory points, located using video records; 3, trajectory.
the acoustic wave was recorded 120–150 s later. As the velocity of sound waves is higher near the Earth’s surface than at some altitude and the wind near the surface was blowing from the explosion site to the city, the horizontal component of velocity was considerably higher in Chelyabinsk than in the villages near the meteoroid trajectory. Hence the large number of broken windows in Chelyabinsk. Precise calculations require known wind velocity at different altitudes and its direction. Unfortunately, we do not have these data at our disposal, but they can be obtained if we analyze the image of smoke from the chimneys. Eyewitnesses in Miass (60–65 km from the explosion epicenter) deny having heard the sound. This is explained by the facts that the shadow zone of the sound wave from the source at an altitude of 21 km began at a distance of 60 km from the epicenter (Fig. 3) and that the wind was blowing from Miass to Chelyabinsk. The radius of the area in which the sound of the explosion could be heard is estimated at 90 km from T2. From T3 (altitude of glow 68 km), the bolide could be seen in an area up to 800 km east of T3 and ~1000 km west. The set of sound waves from this path segment formed the sound wave which was recorded worldwide (http://www.iris. edu/dms/nodes/dmc/specialevents/2013/02/19/chelyabinsk-ru s-sia-bolide-meteor/#sthash.7NCko4fy.dpuf).
Seismic effects The meteoroid fragments showered down on an area no less than 20 km in size latitudinally and 40 km longitudinally. Only the waves resulting from the fall of the sound wave to the Earth’s surface were recorded at the Arti (ARU) and
Fig. 2. Critical frequencies of ionospheric layers E, F1, and F2 the day before and during the meteoroid passage. 1, moment of the meteoroid passage; 2, 3, data for 14 and 15 February 2013, respectively; 4, month average critical frequencies of layer F2 with a standard deviation.
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V.S. Seleznev et al. / Russian Geology and Geophysics 55 (2014) 405–410
Fig. 3. Calculation of the propagation parameters of acoustic waves from the meteoroid explosion in the atmosphere. a, Speed of sound vs. altitude; b, time–distance curves for the acoustic waves at different altitudes of the source; c, ray trajectories at source altitudes of 25 and 30 km. 1, values after (State Standard 44-01, 1981); 2, interpolated values; 3, source altitude (km).
Sverdlovsk (SVE) seismic stations, whereas earlier times did not permit reliable determination of the arrivals of any waves. We can only give a rough estimate of the maximum possible seismic energy of the earthquake caused by the fall of the meteoroid fragments. The application of approaches used in seismology to determine the energy of earthquake foci showed that the maximum possible energy of the earthquake did not exceed class 9 (otherwise, the seismic-wave arrivals would be conspicuous against the background of the microseisms on seismograms).
Unique records are available from the seismic stations of IRIS GSN/University of California San Diego, the CentralAsian Real-Time Earthquake Monitoring Network, GFZ Potsdam, the Kazakhstan National Data Center, the Geophysical Survey RAS, and the Geophysical Survey SB RAS (Fig. 4). Waves of this type are produced by atmospheric nuclear and thermonuclear explosions (Kogan, 1975). However, these are point sources, whereas the source in the case of the Chelyabinsk meteoroid extended for 33.7 km.
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Fig. 4. Arrangement of broadband seismic stations (a) and seismograms with a record of a vertical surface wave (b). 1, epicenter of the meteoroid explosion; 2, seismic stations. t, Time; L, epicentral distance (km); v, reduction rate (3.15 km/s); v*, apparent velocity of the surface wave; ∆, epicentral distance.
The explosion energy was estimated from the surface-wave amplitude by the technique described in (Kogan, 1975). In accordance with this technique, we used a theoretical dependence between the dimensionless energy of the Rayleigh wave and the explosion energy in the case of a high-altitude (30 km) source (Fig. 5). Data from five broadband stations were used to calculate the Rayleigh-wave energy (ER) and the nondimensionalizing parameter F. The figure shows that the explosion energy is 70 to 140 kilotons at different stations, the average value being ~100 kilotons. We emphasize that this estimate presupposes a point source. The reconstruction of the seismic picture requires an accurate time correlation of the events accompanying the meteoroid passage. The timing accuracy on the seismic records is usually higher than 1 ms. The time on the dashcams was taken almost arbitrarily, except the records from the surveillance cameras in Revolution Square and Victory Avenue. If our determination of the meteoroid trajectory is correct, the
distance from the center of segment T1–T2 (lake near Shumakovo Village) to the surveillance cameras is 24 km and the arrival time of the sound wave is 77 s. The time in the source, calculated from the surface-wave arrivals at the closest stations, is 3:21:51 UTC (Fig. 4). Consequently, the explosion took place at 03:20:34 UTC, according to the seismic data. The meteoroid became visible in the atmosphere at 3:20:20 UTC (because 14 s passed from the start of the glow to the explosion). This suggests that the clocks on the surveillance cameras in Revolution Square and Victory Avenue showed correct time and our calculations are accurate.
Conclusions Waves of unusual nature are observed on the seismograms, but the number of the stations is too small to carry out their reliable correlation or to find out their physical origin. Most
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Also, the excitation of waves by the meteoric body is an important issue: It might have excited both acoustic and ion plasma waves. However, waves of all these types attenuate very strongly when the wavelength is close to, or shorter than, the free path. Therefore, these waves have no significant effect on the processes going on near the body (Al’pert et al., 1963). Nevertheless, the passage of the Chelyabinsk meteoroid might have created conditions for the propagation of such waves toward the Earth, which yielded the unusual waves on the seismograms. Modeling of the process might provide a clue to many problems that arose during the primary processing of the data. Data obtained during such events should be stored for subsequent detailed analysis. As the seismic data from the Geophysical Survey SB RAS might not be available to all researchers, we compiled a database (ftp://ftp.gs.sbras.ru/pub/ meteor/). In addition, it contains freeze frames with drawings used to determine the meteoroid trajectory. The authors thank A.G. Yakovlev for help with the plotting of the time-distance curves for the sound waves at different source altitudes. Fig. 5. To the determination of the energy (Q) of the meteoroid explosion using the dependence on the dimensionless energy (ER/F) of a surface wave, after (Kogan, 1975).
likely, the meteoric body moved in the sky over Novosibirsk with supersonic speed through a strongly rarefied medium (the traveltime path of the particles is long compared to its size). Ordinary methods of hydrodynamics or aerodynamics cannot be used to describe the effects in the vicinity of the body in such a rarefied medium, so that the kinetic theory is required.
References Al’pert, Ya.L., Gurevich, A.V., Pitaevskii, L.P., 1963. Effects induced by fast-moving artificial satellite in ionosphere or interplanetary media. Uspekhi Fizicheskikh Nauk 79 (1), 23–80. Kogan, S.Ya., 1975. Seismic Energy and Methods for Its Determination [in Russian]. Nauka, Moscow. State Standard 44-01, 1981. Standard Atmosphere. Parameters. Introduction 01.07.82 [in Russian]. Izd. Standartov, Moscow.
Editorial responsibility: M.I. Epov