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On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach
Geodesy and Geodynamics xxx (xxxx) xxx
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On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach N.V. Silacheva*, U.K. Kulbayeva, N.A. Kravchenko Institute of Seismology, Kazakhstan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 April 2019 Accepted 29 July 2019 Available online xxx
Seismic microzonation for Almaty city for the first time use probabilistic approach and hazard is expressed in terms of not only macroseismic intensity, but also Peak Ground Acceleration (PGA). To account for the effects of local soil conditions, the continual approach proposed by A.S. Aleshin [1, 2] was used, in which soil coefficients are a function of the continuously changing seismic rigidity. Soil coefficients were calculated using the new data of geological and geophysical surveys and findings of previous geotechnical studies. The used approach made it possible to avoid using soil categories and a jump change in characteristics of soil conditions and seismic impact. The developed seismic microzonation maps are prepared for further introduction into the normative documents of the Republic of Kazakhstan. © 2019 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Seismic microzonation maps Peak ground acceleration Soil conditions Seismic rigidity Continual theory
1. Introduction At present, Kazakhstan is undertaking a seismic hazard assessment and seismic micro-zoning approach using a methodology that has not been applied before in the country. The ‘Probabilistic Maps of the General Seismic Zoning of the Kazakhstan territory’ meet the main requirements of Eurocode 8 [3] and were introduced into the Building Regulations “Construction in Seismic Zones” of the Republic of Kazakhstan [4] in 2017. Seismic microzonation for the territory of Almaty city has been completed as part of this work and is the focus of this paper. The new maps are probabilistic and express the hazard estimates in terms of not only traditional for Kazakhstan macroseismic intensity, but also in quantitative parameter (peak ground acceleration). The microzonation was performed by the Institute of Seismology Limited Lability Partnership (LLP) with the involvement at * Corresponding author. E-mail address: [email protected] (N.V. Silacheva). Peer review under responsibility of Institute of Seismology, China Earthquake Administration.
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different stages of the Kazakh Research Institute of Earthquake Engineering and Architecture LLP (KazNIISA), the Kazakh Geotechnical Institute of Surveys LLP (KazGIIZ) and the Institute of Geophysical Research RSE (IGI). A number of different maps were produced that are organized into a main set and an additional set. The main set consists of five maps: Map of Peak Ground Accelerations (PGA) for practical use, intended for direct use in construction calculations; Probabilistic Maps of Seismic Microzonation (SMZ) in terms of [5] macroseismic intensity (MSK-64(K)) for two probabilities of exceedance: 10% and 2% in 50 years; Map of Soil Categories by Seismic Properties; Map of Geotechnical Zoning. The additional set includes: Background (for ‘medium’ site conditions) Seismic Hazard Maps in terms of macroseismic intensity (MSK 64(K)) for exceedance probabilities of 10% and 2% in 50 years; Background (for rock) Seismic Hazard Maps in terms of PGA for probabilities of exceedance of 10% and 2% in 50 years; Probabilistic Maps of Seismic Microzonation in PGA for the same exceedance probabilities; Map of Vs30 for Almaty (average shear wave velocity in the top 30 m);
https://doi.org/10.1016/j.geog.2019.07.006 1674-9847/© 2019 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Map of Average Intensity Increments obtained with the seismic rigidity method [6]; Map of the actual materials showing the locations of the boreholes where stratigraphic data were obtained. The microzonation project consisted of two tasks: (1) probabilistic assessment of the background seismic hazard and (2) the development of seismic microzonation maps using the findings of geotechnical and instrumental geophysical surveys carried out by KazGIIZ. Our group was responsible for hazard analysis and developing maps in terms of PGA. The background seismic hazard assessment for Almaty was carried out on the basis of the methodology complying with the main provisions of Eurocode 8 “Design of seismic resistant structures” [3]. This work is described in detail in [7] and the current paper focuses on integrating site effects into the results. However, to summarize, the main differences between what EC8 requires (and is described in [7]) and what has been done in the past for Kazakhstan is the use of probabilistic seismic hazard assessment (PSHA) and the expression of hazard estimates in terms of not only macroseismic intensity but also engineering parameters such as PGA. The database used in the hazard assessment included updated earthquake catalogs, a revised seismic source model and recent ground motion prediction equations. A Monte Carlo approach was used to compute the hazard [8]. This gives the same results as the traditional Cornell method [8,9]. The PSHA procedure included four main steps: identification and characterization of the potential earthquake sources: computation of the annual number of earthquakes in each seismic source using the catalogue of earthquakes; computation of ground motion produced at the site; and estimation of the probability that the ground motion will be exceeded during a particular time periods. The outputs from the first task were seismic hazard maps for the territory of Almaty (the study area is shown in Fig. 1) in PGA for two probabilities of exceedance: 10% in 50 years (corresponding to a return period of 475 years) and 2% in 50 years (or a return period of 2475 years). The calculations were made assuming rock site conditions with seismic rigidity R ¼ 2000 t/(m2$s) and Vs30 ¼ 800 m/s, r ¼ 2.5 t/m3. These maps are shown in Fig. 2. For a return period of 475 years (Fig. 2 on the left), the PGA relatively evenly increases in the south-east direction from 0.31 g on the northwestern border of the city to 0.62 g in the mountainous
part on the southeastern border. The most built-up part of the city lies within the contours of 0.32e0.45 g. On the map for a return period of 2475 years (Fig. 2 on the right), the increase in PGA maintains its south-easterly direction, but its character slightly changes as the large infrequent earthquakes in the high mountains start to dominate the hazard. The most built-up part of the city lies within the contours of 0.6e0.9 g. 2. Incorporating local site effects In the United States and other western countries, from the very beginning seismic zoning was carried out in instrumental parameters (PGA, spectral accelerations, etc.) and under the patronage of civil engineers. In the post-soviet countries, macroseismic intensity was initially the main output parameter describing seismic impact. The conversion of the macroseismic intensity into quantitative parameters such as PGA, spectral accelerations, etc. was carried out in building codes and regulations. Macrosesimic intensity has also been used in Kazakhstan's building codes. Mapping of the background seismic hazard and microzonation was carried out only for intensity (according to the MSK-64(K) scale [5]), which incorrectly reflected the relationship between intensity scores and accelerations [10,11]. To overcome the drawbacks of outdated methods, a new revised seismic intensity scale was developed in Russia [10,11]. Transition to using instrumental ground motion measures and using site factors rather than intensity increments to account for soil conditions was started. New Russian building codes are now being developed using the parameters of a seismic impact and a soil massif, continuously distributed in space [12]. For the new microzonation of Almaty, the seismic hazard assessment in terms of PGA was carried out independently of the assessment for macroseismic intensity so that the site effects could be also accounted in accelerations directly and not indirectly from intensity as has been done in the past. In this study, we have used the method developed by Aleshin based on his continual theory of microzonation [1,2]. The integration of site effects into PSHA is still an open issue within the seismic hazard community [13]. Several approaches have been proposed varying from deterministic to fully probabilistic, through hybrid (probabilistic-deterministic) approaches. Various approaches to incorporate the site response into a PSHA, including both straightforward but less rigorous approaches and
Fig. 1. Map of south-eastern Kazakhstan showing the study area and seismicity (4 Mw 8, from 250 BC to 2018). The rectangle shows the territory around Almaty city that included seismic sources considered in the hazard assessment.
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
N.V. Silacheva et al. / Geodesy and Geodynamics xxx (xxxx) xxx
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Fig. 2. The background seismic hazard maps of Almaty city in terms of PGA for return periods of 475 years (left) and 2475 years (right), and assuming rock site conditions.
complex probabilistic methods are considered in [14]. The approach applied for Almaty microzonation may be referred to the hybrid ones. PSHA on rock was multiplied by a frequency dependent soil factor (a function of Vs30 and soil density). Soil factors were determined [1] on the base of computer modelling of the influence of soil properties, represented by seismic rigidity R (product of Vs30 and soil density r30) [15], on seismic effect parameters in the form of soil factors. The determined model values of soil factors for high frequency range are close to Fa values used in the American BC [16]. In [16] both seismic impact and soil properties are determined in the tabular form, i.e. they are discrete in terms of the soil categories from A to E, and the transition from one class to another (for example, the impact level) is accompanied by a jump. Aleshin [1,2] shows that this form of representation contradicts the nature of objects that are continuous. The level of the background impact is characterized by a continuous value of the maximum acceleration. Soil coefficients depend on the shear wave velocity, which is the most important characteristic of soil categories in both US and Russian standards. The characteristics of the seismic impact (in the form of soil coefficients) show a continuous dependence on the properties of soil, expressed in terms of Vs30. Aleshin's [1,2] approach takes into account the fact that the soil response to ground shaking is determined by the seismic rigidity [15]. The soil coefficients for the short-period and long-period parts of the spectrum can be related to seismic rigidity through Equations (1) and (2): log Fa ¼ 0.4 log R þ 1.32
(1)
log Fv ¼ 0.6 log R þ 2
(2)
Thus, the use of the soil category concept becomes redundant and the seismic properties of the medium can be adequately described by continuous values of the seismic rigidities. The multiplicative site coefficient equaled one corresponds to rocks with
seismic rigidity of 2000 t/(m2$s). This approach avoids the need to convert from intensity to PGA, and vice versa, and the influence of local site conditions can be directly computed using measurements of shear wave velocity and density obtained by geotechnical and instrumental geophysical surveys. Nonlinear behavior was accounted by using the coefficients presented in Table 1, which are taken from [12]. For the loose soil they reduce PGA level too much and for soils with Vs30 < 270 m/s the recommendations of [17] were taken into account. Diagram of the effect of soil stiffness degradation on the values of peak accelerations according to [17] is shown in the Fig. 3. The coefficients for accounting for topography (slope steepness more than 15 and more than 30 ) were not taken into account but can be introduced separately when developing regulatory documents, for example, as was done in [4]. 3. Geological and geophysical basis The city of Almaty is located in the foothills zone of the Zaili Alatau Mountains, which is one of the most earthquake-prone areas of Central Asia and on the territory of a deep sedimentary basin. The Almaty Basin comprises a complex of PaleogeneNeogene and Quaternary-aged unconsolidated sediments (and cover soils), which unconformably lie on top of Paleozoic-aged
Table 1 Coefficients to account for nonlinear behavior (from Ref. [12]). Seismic rigidity t/(m2$s)
Initial seismic acceleration (g) for rock condition (Vs30 ¼ 800 m/s) 0.25
0.5
0.75
1.0
1.25
200 600 1300 2000
1 1 1 1
0.7 0.9 1 1
0.5 0.75 0.9 1
0.45 0.7 0.85 1
0.4 0.6 0.8 1
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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(selected according to the drilling data) were determined. The average Vs30 values in archival seismic probes were calculated. The ratios of the average Vs30 and Vs10 values in areas with different geotechnical properties of soils were obtained. The Map of Soil Categories by Seismic Properties was compiled on the base of geotechnical surveys and seismic sounding (Fig. 4). 4. Microzonation maps for Almaty The average shear wave velocities and densities for the top 30 m obtained at 1451 sites across Almaty were used to determine seismic rigidity. Average Vs30 and r30 were calculated with use of the following relationships:
30 Vs30 ¼ PN h
i
(3)
i¼1 Vi
Fig. 3. The effect of soil stiffness on peak accelerations (modified from [17]). I- rock, II e stiff soil, III e «medium soil», IV e soft soil.
basement rocks. Paleogene-Neogene deposits lie on the Paleozoic basement and are characterized by a uniform composition. Quaternary-aged sediments are present in intermountain depressions and comprise repeated alternations of pebbles, sands, sandy loams and loams. The Quaternary successions are divided into the ‘lower’-, ‘middle’-, and ‘upper’-quaternary. The depth of the Paleozoic basement varies below Almaty from 1 to 4 km, with the maximum depth to basement in the north-eastern part of the city. The basement shallows towards the north of Almaty reaching a depth of 2.5 km, and to the southern part of the city where it is present near to the land surface. KazGIIZ and IGI carried out geological and geophysical surveys to compile data on the local site conditions. The findings from engineering and geological surveys carried out during previous microzonations were brought together. These data were supplemented by data obtained during the drilling of new boreholes and laboratory tests of cores, geophysical profiles to determine the velocity structure in the studied areas and mapping of tectonic faults. A range of geophysical methods were used included seismic refraction surveying, vertical electrical sounding (resistivity) and ground penetrating radar. To ensure a mapping scale of 1:25000, 3e4 boreholes per 1 km2 were required. A total of 626 archive boreholes were used and 68 new boreholes were drilled. For the purposes of geotechnical zoning, three different scales were defined - regions, sub-regions, and sites. A ‘region’ is distinguished by its geomorphological features and is characterized by general features of the geological structure, hydrogeological conditions and physical-geological processes. A region is divided into ‘sub-regions’ according to the lithological composition and thickness of the soil layers. Within the sub-regions, sites are distinguished by groundwater level. From this, the typification of soil conditions was made. At some sites, the method of geotechnical analogies was used for microzonation using data available from geotechnical surveys. The results of previous work to develop microzonation for Almaty city were taken into account for geotechnical microzonation. A map of geotechnical zoning of the city was compiled. To develop the Map of the Shear Waves Velocities in a 30-meter soil massif, the data from 773 archival seismic probes were used. These probes were evenly distributed over the territory with an average density of 1e2 seismic probes per square kilometer and 70 new seismic probes were added. The seismic probes were located near geological boreholes that describe the geotechnical section down to 30 m depth in detail. According to the measured shear wave velocities, the shear wave velocities in each geotechnical layer
30
rs30 ¼ PN
hi i¼1 ri
(4)
where hi, Vi and ri are the depth (in meters), shear wave velocity and density of a soil layer i. N is the total number of layers in 30 m soil massif. The areal distribution of the obtained rigidity values is shown in Fig. 5. The influence of ground conditions on ground shaking was taken into account using the soil coefficient for the short-period part of a spectrum. According to recommendations [1,2] included in [12], the dependence of soil coefficients Fa on seismic rigidity R in a linear range (background acceleration does not exceed 0.25 g) was calculated using Equation (1). At higher background accelerations for soils with Vs30 270 m/s, the nonlinearity coefficient recommended by [12] was taken into account. For loose soils (Vs30 < 270 m/s) the PGA was limited to a maximum value of 0.675 g according to recommendations [17]. To contour the data, the kriging method was applied to the ground accelerations calculated at the locations of the seismic probes shown in Fig. 5. It is important to note that since the sites are not uniformly distributed, the interpolation method can create distortions. The obtained maps (maps of accelerations for practical use and SMZ) were corrected taking into account the Map of Soil Categories by Seismic Properties (Fig. 4) and the Map of Geotechnical Zoning of the territory of Almaty provided by KazGIIZ. The final microzonation maps shown in Fig. 6 are given in terms of PGA (the average geometric mean) measured in g. The contours are drawn at intervals 0.025 g. Within the intervals, the values increase unevenly. The microzonation maps differ significantly from the background seismic hazard maps calculated assuming Vs30 ¼ 800 m/s across the city. In the territory of Almaty the lowest hazard on these maps is observed for an area of debris cone deposits, which lies between the Almaty and Diagonal faults. At 475 years (Fig. 3, left), the PGA hazard here is between 0.375 and 0.675 g. A somewhat higher level of hazard is obtained in the northwestern part of the city north of the Boroldai Fault. Here, at the lowest background seismicity, the amplification is relatively small, and the total PGA is up to 0.51 g. In the piedmont mountain area (north of the Zaili Fault) PGA varies from 0.53 to 0.675 g. In the territory to the south of the Zaili fault, which entered the new boundary of the city, the PGA level on rocks varies from 0.5 to 0.675 g. High PGA values are also noted in the northern part of the city between the Almaty and Boroldai faults. Here the maximum PGA values are mostly limited by the non-linear behavior of soft soils. Spot-like variations of low and high PGA values are due to the difference
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Fig. 4. Scheme of [4] soil categories by seismic properties (modified from the Map of Soil Categories by Seismic Properties developed by KazGIIZ). IA: Vs30 800 m/s; IB: Vs10 350 m/s, 550 Vs30 < 800 m/s; II: 230 Vs10 < 350 m/s; 270 Vs30 < 550 m/s; III: Vs10 < 230 m/s, Vs30 < 270 m/s.
Fig. 5. Estimates of seismic rigidity determined from Vs30 and density data. Red dots show the locations of seismic probe sites.
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Fig. 6. Seismic micro-zoning maps for Almaty city in terms of PGA for a probability of exceedance of 10% in 50 years (left) and 2% in 50 years (right). Gray strips indicate the location of the main tectonic faults within the city.
in soil amplification. A chain of spots with a high PGA level stretches along the Almaty Fault. On the map with recurrence period 475 years, PGA varies in this zone from 0.54 g to 0.57 g, taking into account nonlinearity. On a map with a 2% probability of exceedance in 50 years (recurrence period 2475 years), shown in Fig. 3 (right), the PGA level is high and practically throughout the city corresponds to a macroseismic intensity of more than 9 MSK. The Map of Accelerations for Practical Use is calculated using the PGA SMZ maps and allows direct using of its values in engineering calculations. For easier use the contour interval is 0.02 g, and the values do not change within the intervals. Acceleration at each point on the map corresponds to the maximum of two values d PGA with a return period of 475 years or 2/3 PGA with a return period of 2475 years. The SMZ map in accelerations for practical use with the specified corrections is shown in Fig. 7. 5. Conclusion The seismic microzonation for Almaty city presented in this study has been carried out as a part of the revision of the construction regulatory framework in Kazakhstan. All previous seismic microzonation maps for Kazakhstan have been based on deterministic assessments of the hazard expressed in terms of macroseismic intensity. The new maps use probabilistic approach and hazard is expressed in terms of not only intensity, but also PGA. To account for the effects of local soil conditions, soil coefficients were used, which are a function of the continuously changing seismic rigidity. These coefficients can be directly applied to PGA values.
The used continual approach made it possible to avoid using soil categories and a jump change in characteristics of soil conditions and seismic impact. Soil coefficients were calculated using the findings of previous geotechnical studies as well as data obtained from new boreholes, laboratory testing of cores, and applying a range of geophysical profiles to determine the velocity section of the studied areas. On the base of the study results of physical and geological characteristics, the typing of soil conditions was performed; for some sites, the method of geotechnical analogies was used. The modern approach is especially important for Almaty, a rapidly developing megalopolis with a population of more than 1.8 million people, where the last seismic microzonation project was carried out more than 30 years ago. The city has a history of large, damaging earthquakes (give dates and magnitudes). Not only it is located in one of the most earthquake-prone regions of the world, but also on a deep sedimentary basin, the geotechnical, geometric and geophysical characteristics of which are favorable for ground motion amplification [18] during strong earthquakes. The results of a probabilistic assessment focused on specified time intervals are best suited for the design of buildings and structures for performance. The use of engineering parameters accepted in world practice meets the needs of earthquake-resistant construction, since they allow using them directly in calculations, rather than transforming macroseismic intensity into the required accelerations, as before. The probabilistic seismic hazard assessment and microzonation in engineering parameters realized for
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
N.V. Silacheva et al. / Geodesy and Geodynamics xxx (xxxx) xxx
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Fig. 7. The map in PGA calculated for practical use (PGA for return period of 475 years or 2/3 PGA for return period 2475 years, whichever is largest) for the territory of Almaty.
Almaty will be an important methodological approach for similar studies in other cities of Kazakhstan.
recommendations on microzonation aspects and the expert of the BGS Dr. S. Sargeant for discussions on PSHA aspects and correcting the English presentation of the text.
Conflict of interests There is no conflict of interests. Acknowledgements Funding was provided through the Ministry of Education and Science. The study was carried out as a part of the project “Development of the Seismic Microzonation Map for the Territory of Almaty City on a New Methodical Base” (state registration No 0115RK02701) and funded within the state funding. Overall project management was carried out by the director of the Institute of Seismology T. Abakanov and the deputy director A. Lee (in 2012e2016) and then the director D. Suleev and the deputy director N. Uzbekov. Moreover the authors would like to express gratitude to the expert of the KAZNIISA Dr. I. E. Itskov for discussions and
References [1] A.S. Aleshin, The Continual Theory of Seismic Microzonation, M.: Nauchnyi mir, 2017, p. 302 (in Russian). [2] A.S. Aleshin, The paradigm of the seismic zonation continuality, World J. Eng. Technol. 3 (2015) 338e343. https://file.scirp.org/pdf/WJET_2015111614550351. pdf. [3] BSEN 1998-1: 2004 Eurocode 8. Design of Structures for Earthquake Resistance - Part 1: General Rules, Seismic Actions and Rules for Buildings, European Committee for Standardization, Brussels, Belgium, 2004. [4] SP RK 2.03-30-2017. Construction in seismic zones, Astana, 2017 (in Russian). [5] SNRK 2.03-28-2004. The Scale for Earthquake Intensity Estimation MSK-64(K), Almaty, 2004 (in Russian). [6] A.S. Aleshin, The new formula of Seismic Rigidity Method, Open J. Civ. Eng. (8) (2018) 326e340. http://www.scirp.org/journal/ojce. [7] N.V. Silacheva, U.K. Kulbayeva, N.A. Kravchenko, Probabilistic seismic hazard assessment of Kazakhstan and Almaty city in peak ground accelerations, Geodesy Geodyn. 9 (2018) 131e141.
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[8] R. Musson, PSHA Using Monte Carlo Simulation: M3C v3 User Guide, Internal Report IR/09/058, British Geological Survey. Personal communications, 2009, p. 31. [9] I. Mosca, B. Baptie, S. Sargeant, R. Walker, Integrating outcomes from probabilistic and deterministic seismic hazard analysis in the tien shan, BSSA 109 (2019) 688e715. [10] F.F. Aptikaev, The Instrumental Scale of Seismic Intensity, Science and education, Moscow, 2012, p. 175p (in Russian). [11] F.F. Aptikaev, O.O. Erteleva, A new generation Russian seismic scale, Seism. Instrum. 53 (No. 2) (2017) 146e154, https://doi.org/10.3103/S074792391 7020025. [12] SP283.1325800.2016 - Building Objects of Increased Responsibility. Seismic Microzonation Rules. M, 2016 (in Russian). bal, P.-Y. Bard, C. Beauval, J.C. Go mez, Integration of site effects into [13] C. Aristiza probabilistic seismic hazard assessment (PSHA): a comparison between two fully probabilistic methods on the euroseistest site, Geosciences 8 (2018) 285, https://doi.org/10.3390/geosciences8080285. [14] S. Barani, D. Spallarossa, Soil amplification in probabilistic ground motion hazard analysis, Bull. Earthq. Eng. (2016), https://doi.org/10.1007/s10518016-9971-y. Springer ScienceþBusiness Media Dordrecht. [15] A.S. Aleshin, The new formula of seismic rigidity method, Open J. Civ. Eng. 8 (2018) 326e340. https://doi.org/10.4236/ojce.2018.83025. [16] BSSC (Building Seismic Safety Council), NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures. Part 1: Provisions, Prepared by the Building Seismic Safety Council for the Federal
Emergency Management Agency (report FEMA 450), 2003, p. 356. Washington, D.C. [17] I.E. Itskov, Suggestions for improving the methodology for taking into account the effect of ground conditions on the design seismic loads, Earthq. Eng. Saf. Facil. 6 (2001) 44e49 (in Russian). [18] M. Pilz, T. Abakanov, K. Abdrakhmatov, D. Bindi, T. Boxberger, B. Moldobekov, S. Orunbayev, N. Silacheva, Sh. Ullah, Sh. Usupaev, P. Yasunov, S. Parolai, An overview on the seismic microzonation and site effect studies in Central Asia, Ann. Geophys. 58 (1) (2015) S0104.
Dr. Natalya Silacheva is a Chief Researcher in the LLC “Institute of Seismology”, Republic of Kazakhstan. She participated in the creation of the first digital strong motion network in Kazakhstan, was engaged in developing a methodological base for its data analysis and compiling a bank of ground motion parameters. She is engaged in seismic hazard assessment in quantitative parameters for sites and territories; in research on local site effects, analysis of soil response and ground motion amplification in the Almaty basin. In the recent projects on the creation of Probabilistic Seismic Zoning Maps of Kazakhstan and Seismic Microzoning Maps of Almaty City she was responsible for probabilistic analysis and development of maps in accelerations.
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach N.V. Silacheva*, U.K. Kulbayeva, N.A. Kravchenko Institute of Seismology, Kazakhstan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 April 2019 Accepted 29 July 2019 Available online xxx
Seismic microzonation for Almaty city for the first time use probabilistic approach and hazard is expressed in terms of not only macroseismic intensity, but also Peak Ground Acceleration (PGA). To account for the effects of local soil conditions, the continual approach proposed by A.S. Aleshin [1, 2] was used, in which soil coefficients are a function of the continuously changing seismic rigidity. Soil coefficients were calculated using the new data of geological and geophysical surveys and findings of previous geotechnical studies. The used approach made it possible to avoid using soil categories and a jump change in characteristics of soil conditions and seismic impact. The developed seismic microzonation maps are prepared for further introduction into the normative documents of the Republic of Kazakhstan. © 2019 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Seismic microzonation maps Peak ground acceleration Soil conditions Seismic rigidity Continual theory
1. Introduction At present, Kazakhstan is undertaking a seismic hazard assessment and seismic micro-zoning approach using a methodology that has not been applied before in the country. The ‘Probabilistic Maps of the General Seismic Zoning of the Kazakhstan territory’ meet the main requirements of Eurocode 8 [3] and were introduced into the Building Regulations “Construction in Seismic Zones” of the Republic of Kazakhstan [4] in 2017. Seismic microzonation for the territory of Almaty city has been completed as part of this work and is the focus of this paper. The new maps are probabilistic and express the hazard estimates in terms of not only traditional for Kazakhstan macroseismic intensity, but also in quantitative parameter (peak ground acceleration). The microzonation was performed by the Institute of Seismology Limited Lability Partnership (LLP) with the involvement at * Corresponding author. E-mail address: [email protected] (N.V. Silacheva). Peer review under responsibility of Institute of Seismology, China Earthquake Administration.
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different stages of the Kazakh Research Institute of Earthquake Engineering and Architecture LLP (KazNIISA), the Kazakh Geotechnical Institute of Surveys LLP (KazGIIZ) and the Institute of Geophysical Research RSE (IGI). A number of different maps were produced that are organized into a main set and an additional set. The main set consists of five maps: Map of Peak Ground Accelerations (PGA) for practical use, intended for direct use in construction calculations; Probabilistic Maps of Seismic Microzonation (SMZ) in terms of [5] macroseismic intensity (MSK-64(K)) for two probabilities of exceedance: 10% and 2% in 50 years; Map of Soil Categories by Seismic Properties; Map of Geotechnical Zoning. The additional set includes: Background (for ‘medium’ site conditions) Seismic Hazard Maps in terms of macroseismic intensity (MSK 64(K)) for exceedance probabilities of 10% and 2% in 50 years; Background (for rock) Seismic Hazard Maps in terms of PGA for probabilities of exceedance of 10% and 2% in 50 years; Probabilistic Maps of Seismic Microzonation in PGA for the same exceedance probabilities; Map of Vs30 for Almaty (average shear wave velocity in the top 30 m);
https://doi.org/10.1016/j.geog.2019.07.006 1674-9847/© 2019 Institute of Seismology, China Earthquake Administration, etc. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Map of Average Intensity Increments obtained with the seismic rigidity method [6]; Map of the actual materials showing the locations of the boreholes where stratigraphic data were obtained. The microzonation project consisted of two tasks: (1) probabilistic assessment of the background seismic hazard and (2) the development of seismic microzonation maps using the findings of geotechnical and instrumental geophysical surveys carried out by KazGIIZ. Our group was responsible for hazard analysis and developing maps in terms of PGA. The background seismic hazard assessment for Almaty was carried out on the basis of the methodology complying with the main provisions of Eurocode 8 “Design of seismic resistant structures” [3]. This work is described in detail in [7] and the current paper focuses on integrating site effects into the results. However, to summarize, the main differences between what EC8 requires (and is described in [7]) and what has been done in the past for Kazakhstan is the use of probabilistic seismic hazard assessment (PSHA) and the expression of hazard estimates in terms of not only macroseismic intensity but also engineering parameters such as PGA. The database used in the hazard assessment included updated earthquake catalogs, a revised seismic source model and recent ground motion prediction equations. A Monte Carlo approach was used to compute the hazard [8]. This gives the same results as the traditional Cornell method [8,9]. The PSHA procedure included four main steps: identification and characterization of the potential earthquake sources: computation of the annual number of earthquakes in each seismic source using the catalogue of earthquakes; computation of ground motion produced at the site; and estimation of the probability that the ground motion will be exceeded during a particular time periods. The outputs from the first task were seismic hazard maps for the territory of Almaty (the study area is shown in Fig. 1) in PGA for two probabilities of exceedance: 10% in 50 years (corresponding to a return period of 475 years) and 2% in 50 years (or a return period of 2475 years). The calculations were made assuming rock site conditions with seismic rigidity R ¼ 2000 t/(m2$s) and Vs30 ¼ 800 m/s, r ¼ 2.5 t/m3. These maps are shown in Fig. 2. For a return period of 475 years (Fig. 2 on the left), the PGA relatively evenly increases in the south-east direction from 0.31 g on the northwestern border of the city to 0.62 g in the mountainous
part on the southeastern border. The most built-up part of the city lies within the contours of 0.32e0.45 g. On the map for a return period of 2475 years (Fig. 2 on the right), the increase in PGA maintains its south-easterly direction, but its character slightly changes as the large infrequent earthquakes in the high mountains start to dominate the hazard. The most built-up part of the city lies within the contours of 0.6e0.9 g. 2. Incorporating local site effects In the United States and other western countries, from the very beginning seismic zoning was carried out in instrumental parameters (PGA, spectral accelerations, etc.) and under the patronage of civil engineers. In the post-soviet countries, macroseismic intensity was initially the main output parameter describing seismic impact. The conversion of the macroseismic intensity into quantitative parameters such as PGA, spectral accelerations, etc. was carried out in building codes and regulations. Macrosesimic intensity has also been used in Kazakhstan's building codes. Mapping of the background seismic hazard and microzonation was carried out only for intensity (according to the MSK-64(K) scale [5]), which incorrectly reflected the relationship between intensity scores and accelerations [10,11]. To overcome the drawbacks of outdated methods, a new revised seismic intensity scale was developed in Russia [10,11]. Transition to using instrumental ground motion measures and using site factors rather than intensity increments to account for soil conditions was started. New Russian building codes are now being developed using the parameters of a seismic impact and a soil massif, continuously distributed in space [12]. For the new microzonation of Almaty, the seismic hazard assessment in terms of PGA was carried out independently of the assessment for macroseismic intensity so that the site effects could be also accounted in accelerations directly and not indirectly from intensity as has been done in the past. In this study, we have used the method developed by Aleshin based on his continual theory of microzonation [1,2]. The integration of site effects into PSHA is still an open issue within the seismic hazard community [13]. Several approaches have been proposed varying from deterministic to fully probabilistic, through hybrid (probabilistic-deterministic) approaches. Various approaches to incorporate the site response into a PSHA, including both straightforward but less rigorous approaches and
Fig. 1. Map of south-eastern Kazakhstan showing the study area and seismicity (4 Mw 8, from 250 BC to 2018). The rectangle shows the territory around Almaty city that included seismic sources considered in the hazard assessment.
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Fig. 2. The background seismic hazard maps of Almaty city in terms of PGA for return periods of 475 years (left) and 2475 years (right), and assuming rock site conditions.
complex probabilistic methods are considered in [14]. The approach applied for Almaty microzonation may be referred to the hybrid ones. PSHA on rock was multiplied by a frequency dependent soil factor (a function of Vs30 and soil density). Soil factors were determined [1] on the base of computer modelling of the influence of soil properties, represented by seismic rigidity R (product of Vs30 and soil density r30) [15], on seismic effect parameters in the form of soil factors. The determined model values of soil factors for high frequency range are close to Fa values used in the American BC [16]. In [16] both seismic impact and soil properties are determined in the tabular form, i.e. they are discrete in terms of the soil categories from A to E, and the transition from one class to another (for example, the impact level) is accompanied by a jump. Aleshin [1,2] shows that this form of representation contradicts the nature of objects that are continuous. The level of the background impact is characterized by a continuous value of the maximum acceleration. Soil coefficients depend on the shear wave velocity, which is the most important characteristic of soil categories in both US and Russian standards. The characteristics of the seismic impact (in the form of soil coefficients) show a continuous dependence on the properties of soil, expressed in terms of Vs30. Aleshin's [1,2] approach takes into account the fact that the soil response to ground shaking is determined by the seismic rigidity [15]. The soil coefficients for the short-period and long-period parts of the spectrum can be related to seismic rigidity through Equations (1) and (2): log Fa ¼ 0.4 log R þ 1.32
(1)
log Fv ¼ 0.6 log R þ 2
(2)
Thus, the use of the soil category concept becomes redundant and the seismic properties of the medium can be adequately described by continuous values of the seismic rigidities. The multiplicative site coefficient equaled one corresponds to rocks with
seismic rigidity of 2000 t/(m2$s). This approach avoids the need to convert from intensity to PGA, and vice versa, and the influence of local site conditions can be directly computed using measurements of shear wave velocity and density obtained by geotechnical and instrumental geophysical surveys. Nonlinear behavior was accounted by using the coefficients presented in Table 1, which are taken from [12]. For the loose soil they reduce PGA level too much and for soils with Vs30 < 270 m/s the recommendations of [17] were taken into account. Diagram of the effect of soil stiffness degradation on the values of peak accelerations according to [17] is shown in the Fig. 3. The coefficients for accounting for topography (slope steepness more than 15 and more than 30 ) were not taken into account but can be introduced separately when developing regulatory documents, for example, as was done in [4]. 3. Geological and geophysical basis The city of Almaty is located in the foothills zone of the Zaili Alatau Mountains, which is one of the most earthquake-prone areas of Central Asia and on the territory of a deep sedimentary basin. The Almaty Basin comprises a complex of PaleogeneNeogene and Quaternary-aged unconsolidated sediments (and cover soils), which unconformably lie on top of Paleozoic-aged
Table 1 Coefficients to account for nonlinear behavior (from Ref. [12]). Seismic rigidity t/(m2$s)
Initial seismic acceleration (g) for rock condition (Vs30 ¼ 800 m/s) 0.25
0.5
0.75
1.0
1.25
200 600 1300 2000
1 1 1 1
0.7 0.9 1 1
0.5 0.75 0.9 1
0.45 0.7 0.85 1
0.4 0.6 0.8 1
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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(selected according to the drilling data) were determined. The average Vs30 values in archival seismic probes were calculated. The ratios of the average Vs30 and Vs10 values in areas with different geotechnical properties of soils were obtained. The Map of Soil Categories by Seismic Properties was compiled on the base of geotechnical surveys and seismic sounding (Fig. 4). 4. Microzonation maps for Almaty The average shear wave velocities and densities for the top 30 m obtained at 1451 sites across Almaty were used to determine seismic rigidity. Average Vs30 and r30 were calculated with use of the following relationships:
30 Vs30 ¼ PN h
i
(3)
i¼1 Vi
Fig. 3. The effect of soil stiffness on peak accelerations (modified from [17]). I- rock, II e stiff soil, III e «medium soil», IV e soft soil.
basement rocks. Paleogene-Neogene deposits lie on the Paleozoic basement and are characterized by a uniform composition. Quaternary-aged sediments are present in intermountain depressions and comprise repeated alternations of pebbles, sands, sandy loams and loams. The Quaternary successions are divided into the ‘lower’-, ‘middle’-, and ‘upper’-quaternary. The depth of the Paleozoic basement varies below Almaty from 1 to 4 km, with the maximum depth to basement in the north-eastern part of the city. The basement shallows towards the north of Almaty reaching a depth of 2.5 km, and to the southern part of the city where it is present near to the land surface. KazGIIZ and IGI carried out geological and geophysical surveys to compile data on the local site conditions. The findings from engineering and geological surveys carried out during previous microzonations were brought together. These data were supplemented by data obtained during the drilling of new boreholes and laboratory tests of cores, geophysical profiles to determine the velocity structure in the studied areas and mapping of tectonic faults. A range of geophysical methods were used included seismic refraction surveying, vertical electrical sounding (resistivity) and ground penetrating radar. To ensure a mapping scale of 1:25000, 3e4 boreholes per 1 km2 were required. A total of 626 archive boreholes were used and 68 new boreholes were drilled. For the purposes of geotechnical zoning, three different scales were defined - regions, sub-regions, and sites. A ‘region’ is distinguished by its geomorphological features and is characterized by general features of the geological structure, hydrogeological conditions and physical-geological processes. A region is divided into ‘sub-regions’ according to the lithological composition and thickness of the soil layers. Within the sub-regions, sites are distinguished by groundwater level. From this, the typification of soil conditions was made. At some sites, the method of geotechnical analogies was used for microzonation using data available from geotechnical surveys. The results of previous work to develop microzonation for Almaty city were taken into account for geotechnical microzonation. A map of geotechnical zoning of the city was compiled. To develop the Map of the Shear Waves Velocities in a 30-meter soil massif, the data from 773 archival seismic probes were used. These probes were evenly distributed over the territory with an average density of 1e2 seismic probes per square kilometer and 70 new seismic probes were added. The seismic probes were located near geological boreholes that describe the geotechnical section down to 30 m depth in detail. According to the measured shear wave velocities, the shear wave velocities in each geotechnical layer
30
rs30 ¼ PN
hi i¼1 ri
(4)
where hi, Vi and ri are the depth (in meters), shear wave velocity and density of a soil layer i. N is the total number of layers in 30 m soil massif. The areal distribution of the obtained rigidity values is shown in Fig. 5. The influence of ground conditions on ground shaking was taken into account using the soil coefficient for the short-period part of a spectrum. According to recommendations [1,2] included in [12], the dependence of soil coefficients Fa on seismic rigidity R in a linear range (background acceleration does not exceed 0.25 g) was calculated using Equation (1). At higher background accelerations for soils with Vs30 270 m/s, the nonlinearity coefficient recommended by [12] was taken into account. For loose soils (Vs30 < 270 m/s) the PGA was limited to a maximum value of 0.675 g according to recommendations [17]. To contour the data, the kriging method was applied to the ground accelerations calculated at the locations of the seismic probes shown in Fig. 5. It is important to note that since the sites are not uniformly distributed, the interpolation method can create distortions. The obtained maps (maps of accelerations for practical use and SMZ) were corrected taking into account the Map of Soil Categories by Seismic Properties (Fig. 4) and the Map of Geotechnical Zoning of the territory of Almaty provided by KazGIIZ. The final microzonation maps shown in Fig. 6 are given in terms of PGA (the average geometric mean) measured in g. The contours are drawn at intervals 0.025 g. Within the intervals, the values increase unevenly. The microzonation maps differ significantly from the background seismic hazard maps calculated assuming Vs30 ¼ 800 m/s across the city. In the territory of Almaty the lowest hazard on these maps is observed for an area of debris cone deposits, which lies between the Almaty and Diagonal faults. At 475 years (Fig. 3, left), the PGA hazard here is between 0.375 and 0.675 g. A somewhat higher level of hazard is obtained in the northwestern part of the city north of the Boroldai Fault. Here, at the lowest background seismicity, the amplification is relatively small, and the total PGA is up to 0.51 g. In the piedmont mountain area (north of the Zaili Fault) PGA varies from 0.53 to 0.675 g. In the territory to the south of the Zaili fault, which entered the new boundary of the city, the PGA level on rocks varies from 0.5 to 0.675 g. High PGA values are also noted in the northern part of the city between the Almaty and Boroldai faults. Here the maximum PGA values are mostly limited by the non-linear behavior of soft soils. Spot-like variations of low and high PGA values are due to the difference
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Fig. 4. Scheme of [4] soil categories by seismic properties (modified from the Map of Soil Categories by Seismic Properties developed by KazGIIZ). IA: Vs30 800 m/s; IB: Vs10 350 m/s, 550 Vs30 < 800 m/s; II: 230 Vs10 < 350 m/s; 270 Vs30 < 550 m/s; III: Vs10 < 230 m/s, Vs30 < 270 m/s.
Fig. 5. Estimates of seismic rigidity determined from Vs30 and density data. Red dots show the locations of seismic probe sites.
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Fig. 6. Seismic micro-zoning maps for Almaty city in terms of PGA for a probability of exceedance of 10% in 50 years (left) and 2% in 50 years (right). Gray strips indicate the location of the main tectonic faults within the city.
in soil amplification. A chain of spots with a high PGA level stretches along the Almaty Fault. On the map with recurrence period 475 years, PGA varies in this zone from 0.54 g to 0.57 g, taking into account nonlinearity. On a map with a 2% probability of exceedance in 50 years (recurrence period 2475 years), shown in Fig. 3 (right), the PGA level is high and practically throughout the city corresponds to a macroseismic intensity of more than 9 MSK. The Map of Accelerations for Practical Use is calculated using the PGA SMZ maps and allows direct using of its values in engineering calculations. For easier use the contour interval is 0.02 g, and the values do not change within the intervals. Acceleration at each point on the map corresponds to the maximum of two values d PGA with a return period of 475 years or 2/3 PGA with a return period of 2475 years. The SMZ map in accelerations for practical use with the specified corrections is shown in Fig. 7. 5. Conclusion The seismic microzonation for Almaty city presented in this study has been carried out as a part of the revision of the construction regulatory framework in Kazakhstan. All previous seismic microzonation maps for Kazakhstan have been based on deterministic assessments of the hazard expressed in terms of macroseismic intensity. The new maps use probabilistic approach and hazard is expressed in terms of not only intensity, but also PGA. To account for the effects of local soil conditions, soil coefficients were used, which are a function of the continuously changing seismic rigidity. These coefficients can be directly applied to PGA values.
The used continual approach made it possible to avoid using soil categories and a jump change in characteristics of soil conditions and seismic impact. Soil coefficients were calculated using the findings of previous geotechnical studies as well as data obtained from new boreholes, laboratory testing of cores, and applying a range of geophysical profiles to determine the velocity section of the studied areas. On the base of the study results of physical and geological characteristics, the typing of soil conditions was performed; for some sites, the method of geotechnical analogies was used. The modern approach is especially important for Almaty, a rapidly developing megalopolis with a population of more than 1.8 million people, where the last seismic microzonation project was carried out more than 30 years ago. The city has a history of large, damaging earthquakes (give dates and magnitudes). Not only it is located in one of the most earthquake-prone regions of the world, but also on a deep sedimentary basin, the geotechnical, geometric and geophysical characteristics of which are favorable for ground motion amplification [18] during strong earthquakes. The results of a probabilistic assessment focused on specified time intervals are best suited for the design of buildings and structures for performance. The use of engineering parameters accepted in world practice meets the needs of earthquake-resistant construction, since they allow using them directly in calculations, rather than transforming macroseismic intensity into the required accelerations, as before. The probabilistic seismic hazard assessment and microzonation in engineering parameters realized for
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006
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Fig. 7. The map in PGA calculated for practical use (PGA for return period of 475 years or 2/3 PGA for return period 2475 years, whichever is largest) for the territory of Almaty.
Almaty will be an important methodological approach for similar studies in other cities of Kazakhstan.
recommendations on microzonation aspects and the expert of the BGS Dr. S. Sargeant for discussions on PSHA aspects and correcting the English presentation of the text.
Conflict of interests There is no conflict of interests. Acknowledgements Funding was provided through the Ministry of Education and Science. The study was carried out as a part of the project “Development of the Seismic Microzonation Map for the Territory of Almaty City on a New Methodical Base” (state registration No 0115RK02701) and funded within the state funding. Overall project management was carried out by the director of the Institute of Seismology T. Abakanov and the deputy director A. Lee (in 2012e2016) and then the director D. Suleev and the deputy director N. Uzbekov. Moreover the authors would like to express gratitude to the expert of the KAZNIISA Dr. I. E. Itskov for discussions and
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[8] R. Musson, PSHA Using Monte Carlo Simulation: M3C v3 User Guide, Internal Report IR/09/058, British Geological Survey. Personal communications, 2009, p. 31. [9] I. Mosca, B. Baptie, S. Sargeant, R. Walker, Integrating outcomes from probabilistic and deterministic seismic hazard analysis in the tien shan, BSSA 109 (2019) 688e715. [10] F.F. Aptikaev, The Instrumental Scale of Seismic Intensity, Science and education, Moscow, 2012, p. 175p (in Russian). [11] F.F. Aptikaev, O.O. Erteleva, A new generation Russian seismic scale, Seism. Instrum. 53 (No. 2) (2017) 146e154, https://doi.org/10.3103/S074792391 7020025. [12] SP283.1325800.2016 - Building Objects of Increased Responsibility. Seismic Microzonation Rules. M, 2016 (in Russian). bal, P.-Y. Bard, C. Beauval, J.C. Go mez, Integration of site effects into [13] C. Aristiza probabilistic seismic hazard assessment (PSHA): a comparison between two fully probabilistic methods on the euroseistest site, Geosciences 8 (2018) 285, https://doi.org/10.3390/geosciences8080285. [14] S. Barani, D. Spallarossa, Soil amplification in probabilistic ground motion hazard analysis, Bull. Earthq. Eng. (2016), https://doi.org/10.1007/s10518016-9971-y. Springer ScienceþBusiness Media Dordrecht. [15] A.S. Aleshin, The new formula of seismic rigidity method, Open J. Civ. Eng. 8 (2018) 326e340. https://doi.org/10.4236/ojce.2018.83025. [16] BSSC (Building Seismic Safety Council), NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures. Part 1: Provisions, Prepared by the Building Seismic Safety Council for the Federal
Emergency Management Agency (report FEMA 450), 2003, p. 356. Washington, D.C. [17] I.E. Itskov, Suggestions for improving the methodology for taking into account the effect of ground conditions on the design seismic loads, Earthq. Eng. Saf. Facil. 6 (2001) 44e49 (in Russian). [18] M. Pilz, T. Abakanov, K. Abdrakhmatov, D. Bindi, T. Boxberger, B. Moldobekov, S. Orunbayev, N. Silacheva, Sh. Ullah, Sh. Usupaev, P. Yasunov, S. Parolai, An overview on the seismic microzonation and site effect studies in Central Asia, Ann. Geophys. 58 (1) (2015) S0104.
Dr. Natalya Silacheva is a Chief Researcher in the LLC “Institute of Seismology”, Republic of Kazakhstan. She participated in the creation of the first digital strong motion network in Kazakhstan, was engaged in developing a methodological base for its data analysis and compiling a bank of ground motion parameters. She is engaged in seismic hazard assessment in quantitative parameters for sites and territories; in research on local site effects, analysis of soil response and ground motion amplification in the Almaty basin. In the recent projects on the creation of Probabilistic Seismic Zoning Maps of Kazakhstan and Seismic Microzoning Maps of Almaty City she was responsible for probabilistic analysis and development of maps in accelerations.
Please cite this article as: N.V. Silacheva et al., On the realization of seismic microzonation of Almaty (Kazakhstan) in ground accelerations based on the “continual” approach, Geodesy and Geodynamics, https://doi.org/10.1016/j.geog.2019.07.006