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Volume 31 Issue 1 March 2018

ISSN 1674-4519 CN 11-5695/P

Adminidrated by: 
China Association of Science and Technology

Sponsored by: 
The Seismological Society of China and Institute of Geophysics, China Earthquake Administration

Editor-in-Chief: Yun-tai Chen

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3D Multi-Parameter Type Traveltime Tomography in a Spherical Coordinate Frame: Comparison of Double and Triple Class Simultaneous Inversions
Chao-ying Bai, Jia-yu Sun, Xing-wang Li, Stewart Greenhalgh
Accepted Manuscript
[Abstract](48) [FullText HTML](20) [PDF 1320KB](9)
Abstract:
It is now common practice to perform simultaneous traveltime inversion for the velocity field and the reflector geometry in reflection/refraction tomography, or the velocity field and the hypocenter locations in regional earthquake tomography, but seldom are all three classes of model parameters updated simultaneously. This is mainly due to the trade-off between the different types of model parameters and the lack of different seismic phases to constrain the model parameters. Using a spherical-coordinate ray tracing algorithm for first and later (primary reflected) arrival tracing algorithm in combination with a popular linearized inversion solver, it is possible to simultaneously recover the three classes of model parameters in regional or global tomographic studies. In this paper we incorporate the multistage irregular shortest-path ray tracing algorithm (in a spherical coordinate system) with a subspace inversion solver to formulate a simultaneous inversion algorithm for triple model parameters updating using direct and later arrival time information. Comparison tests for two sets of data (noise free and added noise) indicate that the new triple-class parameter inversion algorithm is capable of obtaining nearly the same results as the double-class parameter inversion scheme. Furthermore, the proposed multi-parameter type inversion method is not sensitive to a modest level of picking error in the traveltime data, and still performs well with a relatively large uncertainty in earthquake hypocentral locations. Thisshows it to be a feasible and promising approach in regional or global tomographic applications.
Numerical simulation of seismic wavefields in TTI media using the rotated staggered-grid compact finite-difference scheme
Bing Bai, Bingshou He, Kairui Li, Huaigu Tang, Jiajia Yang
Uncorrected proof
[Abstract](122) [FullText HTML](83) [PDF 1305KB](7)
Abstract:
Numerical simulation in transverse isotropic media with tilted symmetry axis (TTI) using the standard staggered-grid finite-difference scheme (SSG) results in errors caused by averaging or interpolation. In order to eliminate the errors, a method of rotated staggered-grid finite-difference scheme (RSG) is proposed. However, the RSG brings serious numerical dispersion. The compact staggered-grid finite-difference scheme (CSG) is an implicit difference scheme, which use fewer grid points to suppress dispersion more effectively than the SSG. This paper combines the CSG with the RSG to derive a rotated staggered-grid compact finite-difference scheme (RSGC). The numerical experiments indicate that the RSGC has weaker numerical dispersion and better accuracy than the RSG.
Review on the study of topographic effect on seismic ground motion
Hong Zhou
Uncorrected proof
[Abstract](97) [FullText HTML](69) [PDF 358KB](6)
Abstract:
Topographic effect study is a very important research topic in seismology, seismic engineering, earthquake engineering, engineering earthquake construction and engineering seismology. This paper focuses on its present development status. Post-earthquake investigation has found that the existence of topography caused more serious earthquake damage. The actual seismographs also recorded the topographic amplification effect of 6 to 7 times and even more than 10 times. Numerical simulation is an important technique to study topographic effect, which complements the lack of observed records. However researches on 3-D topographic effect are not enough and need to be studied deeper. To find the main influence factors and the quantitative relationship between topography and ground motion are required very urgently. Obviously the achievements not only can be applied in the earthquake resistant design, but also can provide the quantitative pre-earthquake disaster prediction and quantitative post-earthquake disaster evaluation.
Modeling and RTM for arbitrary-order pure acoustic wave equation in VTI media using normalized pseudo-analytical method
Shigang Xu, Yang Liu
Uncorrected proof
[Abstract](87) [FullText HTML](68) [PDF 1215KB](2)
Abstract:
The conventional pseudo-acoustic wave equations (PWEs) in vertical transversely isotropic (VTI) media may generate SV-wave artifacts and propagation instabilities when anisotropy parameters cannot satisfy the pseudo-acoustic assumption. One solution to these issues is to use pure acoustic anisotropic wave equations, which can produce stable and pure P-wave responses without any SV-wave pollutions. The commonly used pure acoustic wave equations (PAWEs) in VTI media are mainly derived from the decoupled P-SV dispersion relation based on first-order Taylor-series expansion (TE), thus they will suffer from accuracy loss in strongly anisotropic media. In this paper, we adopt arbitrary-order TE to expand the square root term in Alkhalifah’s accurate acoustic VTI dispersion relation and solve the corresponding PAWE using the normalized pseudo-analytical method (NPAM) based on optimized pseudo-differential operator. Our analysis of phase velocity errors indicates that the accuracy of our new expression is perfectly acceptable for majority anisotropy parameters. The effectiveness of our proposed scheme also can be demonstrated by several numerical examples and reverse-time migration (RTM) result.
Analytic wave series solution of out-of-plane (SH) waves diffraction by an almost semi-circular shallow cylindrical hill
Chunyang Ji, Vincent Lee
Uncorrected proof
[Abstract](109) [FullText HTML](73) [PDF 9639KB](3)
Abstract:
A closed-form wave equation analytic solution of two-dimensional scattering and diffraction of out-of-plane (SH) waves by an almost semi-circular shallow cylindrical hill on a flat, elastic and homogeneous half space is proposed by applying the discrete Fourier series expansions of sine and cosine functions. The semi-circular hill problem is discussed as a special case for the new formulated equation. Compared with the previous semi-circular cases solutions, the present method can give surface displacement amplitudes which agrees well with previous results. Although the proposed equation can now solve the problem of SH-waves diffracted by almost semi-circular shallow hills, the stress and displacement residual amplitudes are numerical insignificantly everywhere. Moreover, the influences of the depth-to-width ratio (a parameter defined in this paper to evaluate the shallowness of the topography of hills) on ground motions are presented and summarized. The limitations and errors of truncation from Graf’s addition theorem and Fourier series equations in the present paper are also discussed.
Dynamic equivalent soil characteristics identification using earthquake records
Asskar Janalizadeh Choobbasti, Saman Soleimani Kutanaei
Uncorrected proof
[Abstract](47) [FullText HTML](29) [PDF 825KB](3)
Abstract:
Techniques for soil property estimation can be categorized into two main groups, in-situ and laboratory methods. Previous investigations indicated that strong ground motions record provides a very useful tool to estimating the in-situ characteristics of soil. The main objective of the present work is to utilize the particle swarm optimization algorithm (PSOA) integrated with linear site response method to obtain the equivalent soil profile characteristics from the available surface and bedrock earthquake motion records. To demonstrate the numerical efficiency and the validity of this approach, the procedure is validated against an available case. Then this procedure is utilized to identify the soil properties profiles of the site by using strong ground motions data recorded during the Bam earthquake of December 26, 2003. The magnitude and PGA of Bam earthquake were MW 6.6 and 0.8 g respectively.
Rupture model of the 2013 Mw 6.6 Lushan (China) earthquake constrained by new GPS data set and its effects on potential seismic hazard
Rumeng Guo, Yong Zheng, Faqi Diao, Xiong Xiong, Jiao Xu
Uncorrected proof
[Abstract](46) [FullText HTML](32) [PDF 1179KB](2)
Abstract:
Vertical records are critical important to determine the rupture model of a earthquake, especially for a thrust earthquake. Due to the relatively lower fitness level of near field vertical displacements, the precision of previous rupture models is relatively lower, and the seismic hazard evaluated thereafter should be further updated. In this work, we applied three-component displacement records from GPS stations in and around the source region of the 2013 Mw 6.6 Lushan earthquake to re-investigate the rupture model. For improving the resolution of the rupture model, both continuous GPS stations and campaign GPS stations were gathered, and secular deformations of the GPS movements were removed from the records of the campaign stations to ensure the reliability of the campaign stations. The rupture model is derived by the steepest descent method (SDM) based on a layered velocity structure. The peak slip value is about 0.75m, with a seismic moment release of 9.89×1018 N·m, equivalent to a Mw 6.60 event. Moreover, the inferred fault geometry coincides with the aftershocks distribution of the Lushan earthquake well. Comparing with previous rupture models, a secondary slip asperity exists in the shallow depth and even touches the ground surface. Based on the distribution of the co-seismic ruptures of Lushan and Wenchuan earthquakes, post-seismic relaxation of Wenchuan earthquake and tectonic loading process, we propose that the seismic hazard is quite high and still needs special attention in the seismic gap between the two earthquakes.
Finite difference calculation of traveltime on non-orthogonal grid
Xiangfang Zeng, Sidao Ni
Uncorrected proof
[Abstract](24) [FullText HTML](22) [PDF 542KB](2)
Abstract:
Finite difference methods have been widely employed in solving the eikonal equation so as to calculate traveltime of seismic phase. Most previous studies used regular orthogonal grid. However, much denser grid is required to sample the interfaces that are undulating in depth direction, such as the Moho and the 660 km discontinuity. Here we propose a new finite difference algorithm to solve the eikonal equation on non-orthogonal grid (irregular grid). To demonstrate its efficiency and accuracy, a test was conducted with a two-layer model. The test result suggests that the similar accuracy of a regular grid with ten times grids could achieve with our new algorithm, but the time cost is only about 0.1 times. A spherical earth model with an undulant 660 km discontinuity was constructed to demonstrate the potential application of our new method. In that case, the traveltime curve fluctuation corresponds to topography. Our new algorithm is efficient in solving the first arrival times of waves associated with undulant interfaces.
Source-independent wave-equation based microseismic source location using traveltime inversion
Songqin Nong, Chao Huang, Liangguo Dong
Uncorrected proof
[Abstract](41) [FullText HTML](44) [PDF 1071KB](4)
Abstract:
A new source location method using wave-equation based traveltime inversion is proposed to locate microseismic events accurately. With a source-independent strategy, microseismic events can be located independently regardless of the accuracy of the source signature and the origin time. The traveltime-residuals-based misfit function has robust performance when the velocity model is inaccurate. The new Fréchet derivatives of the misfit function with respect to source location are derived directly based on the acoustic wave-equation, accounting for the influence of geometrical perturbation and spatial velocity variation. Unlike the mostly used traveltime inversion methods, no traveltime picking or ray tracing is needed. Additionally, the improved scattering-integral method is applied to reduce the computational cost. Numerical tests show the validity of the proposed method.

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Seismic hazard assessment of Tehran, Iran with emphasis on near-fault rupture directivity effects
Ehsan Bazarchi, Reza Saberi, Majid Alinejad
2018, 31(1): 1-11.   doi: 10.29382/eqs-2018-0001-1
[Abstract](357) [FullText HTML](91) [PDF 2756KB](22)
Abstract:
Many destructive earthquakes happened in Tehran, Iran in the last centuries. The existence of active faults like the North Tehran is the main cause of seismicity in this city. According to past investigations, it is estimated that in the scenario of activation of the North Tehran fault, many structures in Tehran will collapse. Therefore, it is necessary to incorporate the near field rupture directivity effects of this fault into the seismic hazard assessment of important sites in Tehran. In this study, using calculations coded in MATLAB, Probabilistic Seismic Hazard Analysis (PSHA) is conducted for an important site in Tehran. Following that, deaggregation technique is performed on PSHA and the contribution of seismic scenarios to hazard is obtained in the range of distance and magnitude. After identifying the North Tehran fault as the most hazardous source affecting the site in 10000-year return period, rupture directivity effects of this fault is incorporated into the seismic hazard assessment using Somerville et al. (1997) model with broadband approach and Shahi and Baker (2011) model with narrowband approach. The results show that the narrowband approach caused a 27% increase in the peak of response spectrum in 10000-year return period compared with the conventional PSHA. Therefore, it is necessary to incorporate the near fault rupture directivity effects into the higher levels of seismic hazard assessment attributed to important sites.
Comparison of strong-motion records and damage implications between the 2014 Yunnan MS6.5 Ludian earthquake and MS6.6 Jinggu earthquake
Peibin Xu, Ruizhi Wen, Yefei Ren
2018, 31(1): 12-18.   doi: 10.29382/eqs-2018-0002-2
[Abstract](96) [FullText HTML](73) [PDF 538KB](2)
Abstract:
Serial destructive earthquakes have caused heavy casualties and economic losses to the city in southwestern of China. The Ludian Ms 6.5 earthquake and the Jinggu Ms 6.6 earthquake occurred in Yunnan province in 2014. There is a question of why the two events with almost the same level of magnitude caused differences in earthquake damage. To understand the uniqueness of the phenomenon, this paper focuses on the characteristics of the ground motions and post-earthquake field investigation for the two events. Firstly, we present an overview of the residuals between the Ludian earthquake and the Jinggu earthquake based on the YW06 Ground Motion Prediction Equation (GMPE), and explain the unusual destructiveness of the strong ground motion. Then we analyze the ground motion recordings at selected typical station, based on the strong motion parameters: equivalent predominant frequency and Arias intensity. The result exhibits a good agreement with the Chinese seismic intensity scale. This study would be helpful to gain a better knowledge of the characteristics and variability of ground motions for MS6 class earthquakes in China and to understand the implications to future earthquakes with similar focal mechanism and local condition.
Weighted residual method for diffraction of plane P-waves in a 2-D elastic half-space III: on an almost circular arbitrary-shaped alluvial valley
Heather P. Brandow, Vincent Lee
2018, 31(1): 19-34.   doi: 10.29382/eqs-2018-0003-3
[Abstract](51) [FullText HTML](29) [PDF 2257KB](2)
Abstract:
Scattering and diffraction of elastic in-plane P- and SV-waves by a surface topography such as an elastic canyon at the surface of a half-space is a classical problem which has been studied by earthquake engineers and strong motion seismologists for over forty years. The case of out-of-plane SH-waves on the same elastic canyon that is semicircular in shape on the half-space surface is the first such problem that was solved by analytic closed-form solutions over forty years ago by Trifunac. The corresponding case of in-plane P- and SV-waves on the same circular canyon is a much more complicated problem because the in-plane P- and SV- scattered waves have different wave speeds and together they must have zero normal and shear stresses at the half-space surface. It is not until recently in 2014 that analytic solution for such problem is found by Lee and Liu. This paper uses their technique of defining these stress-free scattered waves, which Brandow and Lee previously used to solve the problem of the scattering and diffraction of these in-plane waves on an almost-circular surface canyon that is arbitrary in shape, to the study of the scattering and diffraction of these in-plane waves on an almost circular arbitrary-shaped alluvial valley.
Diurnal characteristics of geoelectric fields and their changes associated with the Alxa Zuoqi MS5.8 earthquake on 15 April 2015 (Inner Mongolia)
Qing Ye, Ye Fan, Xuebin Du, Tengfa Cui, Kechang Zhou, Ramesh P. Singh
2018, 31(1): 35-43.   doi: 10.29382/eqs-2018-0004-4
[Abstract](55) [FullText HTML](30) [PDF 2645KB](5)
Abstract:
In China, efforts are being made to monitor geoelectric fields through a large network of stations deployed and managed by the China Earthquake Administration. The diurnal variations in the geoelectric field waveforms were similar in the quiet magnetic periods when K<5 (generally,K<3 indicates a quiet time). The arrival time points of the maxima in the geoelectric field waveforms exhibited differences in local time related to geographic longitude. The amplitude of diurnal variation was several to 16.6 mV/km and decreased with increasing latitude. Further, the amplitude of diurnal variation, which was related to seasonal changes, was larger in summer and autumn than in spring and winter. The periods of diurnal changes during quiet days were 24, 12, 8, 6, 4 hours and several minutes over large areas. Finally, the observed diurnal variations in geoelectric field prior to the Alxa ZuoqiMS5.8 earthquake on 15 April 2015 were studied, and pronounced changes in the spectral values of the geoelectric fields were found to be associated with the Alxa Zuoqi earthquake in Inner Mongolia.
Seismic electric signals in seismic prone areas
Nicholas V. Sarlis, Panayiotis A. Varotsos, Efthimios S. Skordas, Seiya Uyeda, Jacques Zlotnicki, Toshiyasu Nagao, Anatoly Rybin, Mary S. Lazaridou-Varotsos, Konstantina A. Papadopoulou
2018, 31(1): 44-51.   doi: 10.29382/eqs-2018-0005-5
[Abstract](270) [FullText HTML](79) [PDF 2362KB](7)
Abstract:
The Varotsos-Alexopoulos-Nomicos (VAN) method of short-term earthquake prediction was introduced in the 1980s. The VAN method enables estimation of the epicenter, magnitude and occurrence time of an impending earthquake by observing transient changes of the electric field of the Earth termed seismic electric signals (SES). Here, we present a few examples of SES observed in various earthquake prone areas worldwide.
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