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| 1 | The Grid Search Algorithm of Tectonic Stress Tensor Based on Focal Mechanism Data and Its Application in the Boundary Zone of China, Vietnam and Laos显示文摘Stress field plays a key role in geodynamics. In this study, an algorithm to determine the stress tensor and its confidence range from focal mechanism data by using grid search method was proposed. The experiment uses artificial focal mechanism data which were generated by extensional, compression and strike-slip stress regime and different level of noise, shows that the precision of the estimated stress tensor based on this algorithm is greatly improved compared with traditional algorithms. This algorithm has three advantages:(1) The global optimal solution of the stress tensor is determined by fine grid search of 1o×1o×1o×0.01 and local minimum value is avoided;(2) precision of focal mechanism data can be considered, i.e., different weight of the focal mechanism data contributes differently to the process of determining stress tensor;(3) the confidence range of the determined stress tensor can be obtained by using F-test. We apply this algorithm in the boundary zone of China, Vietnam and Laos, and obtain the stress field with SSE-NNW compressive stress direction and NEE-SWW extensional stress direction. The stress ratio is 0.6, which shows that the eigen values of the stress tensor are nearly in arithmetic sequence. The stress field in this region is consistent with the left-lateral strike slip of the Dienbien-Lauangphrabang arc fault. The result will be helpful in studying the geological dynamic process in this region. | Yongge Wan Shuzhong Sheng Jichao Huang Xiang Li Xin Chen | 2016 | Journal of Earth Science2016，27，5： | 48 |
| 2 | Seismological evidence for the convergence of crustal stress orientation before large earthquakes显示文摘Earthquakes are caused by the failure of faults,driven by tectonic stress build-up in the Earth’s crust.To study the earthquake preparation process and assess regional earthquake potentials,it is vitally important to understand the crustal stress evolution process and identify its change in pattern associated with the seismogenic process.In this study we investigate the focal mechanism orientations of earthquakes in southern California from 1982 to 1999,basing on a focal mechanism catalog from Hauksson.We find that for the two large earthquakes occurred in southern California,the 1992 MW7.3 Landers and the 1999 MW7.1 Hector Mine,the orientations of focal mechanisms near the coming earthquake tend to converge to the stress direction promoting the rupture of the coming earthquake and align with its focal mechanism about half-year before its occurrence,suggesting that the tectonic stress field gets more organized in favor of the rupture of the event pre-seismically. The degree of stress convergence is measured by the orientation angle RMS(root mean square)between the preshocks’focal mechanisms and the focal mechanism of the large event studied,and its time series recorded the stress convergence process. The degree of anomalies,measured by the F-tests,indicates that the convergence of stress orientations become significant at 90%confidence about half-year prior to both the Landers and Hector Mine quakes,and it becomes even more prominent at 99%confidence right before the occurrences.Our study may be of significance for assessment of regional seismic potentials. | Yongge Wan | 2009 | Earthquake Science2009，22，6： | 10 |
| 3 | Fault plane parameters of Sanhe-Pinggu M8 earthquake in 1679 determined using present-day small earthquakes显示文摘The great Sanhe-Pinggu M8 earthquake occurred in 1679 was the largest surface rupture event recorded in history in the northern part of North China plain. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method.Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake, and referring to the morphology of the long axis of the isoseismal line obtained by the predecessors, we selected a strip-shaped zone from the relocated earthquake catalog in the period from 1980 to 2009 to invert fault plane parameters of this earthquake. The inversion results are as follows: the strike is 38.23°, the dip angle is 82.54°,the slip angle is-156.08°, the fault length is about 80 km,the lower-boundary depth is about 23 km and the buried depth of upper boundary is about 3 km. This shows that the seismogenic fault is a NNE-trending normal dip-slip fault,southeast wall downward and northwest wall uplift, with the right-lateral strike-slip component. Moreover, the surface rupture zone, intensity distribution of the earthquake and seismic-wave velocity profile in the focal area all verified our study result. | Xiaoshan Wang Xiangdong Feng Xiwei Xu Guiling Diao Yongge Wan Libin Wang Guangqing Ma | 2014 | Earthquake Science2014，27，6： | 9 |
| 4 | Crustal Stress Evolution over the Past 700 Years in North China and Earthquake Occurrence显示文摘Fault interaction and earthquake occurrence have attracted much attention in seismological community during recent years. Many studies have shown that the rupture of one fault could encourage or discourage earthquake nucleation on a neighboring fault, depending on the relative geometry of the two faults and the earthquake rupture mechanisms. In this paper, we simulate the evolutionary process of cumulative Coulomb failure stress change (CCFSC) in North China since 1303, manifested by secular tectonic stress loading and occurrence of large earthquakes. Secular tectonic stress loading is averaged from crustal strain rates derived from GPS. Fault rupture parameters of historical earthquakes are estimated as follows: the earthquake rupture length and the amount of slip are derived based on their statistical relationships with the earthquake intensity distribution and magnitude, calibrated using parameters of instrumentally measured contemporary earthquakes. The earthquake rake angle is derived based on geologically determined fault orientational parameters and seismically estimated orientation of regional tectonic stresses. Assuming a layered visco-elastic medium, we calculate stress evolution resulting from secular tectonic loading and coseismic and postseismic deformation. On the eve of each large earthquake, the accumulated stress field is projected to the fault surface of that earthquake and the CCFSC is evaluated to assess the triggering effect of CCFSC. Forty-nine earthquakes with M≥6.5 have occurred in North China since 1303. Statistics shows that 39 out of the 48 subsequent events were triggered by positive CCFSC, yielding a triggering rate of 81.3%. If we use the accumulative stress field to evaluate the CCFSC for the M≥5.0 earthquakes that occurred in North China since 1303, we find that 75.5% of those events were triggered. The triggering rate for the M≥5.0 earthquakes after the 1976 Ninghe earthquake is up to 82.1%. The triggering rates can be higher if corrections are made for some aftershocks which were wrongly identified as occurring in stress shadow zones because of errors in parameter estimates of historical earthquakes. Our study shows a very high correlation between positive CCFSC and earthquake occurrences. Relatively high CCFSC in North China at present is concentrated around the Bohai Sea, the west segment of the Northern Qinling fault, the western end of the Zhangjiakou-Bohai Sea seismic zone, and the Taiyuan basin, Shanxi graben, suggesting relatively higher earthquake potential in these areas. | Wan Yongge Shen Zhengkang Shang Dan Li Tieming Zeng Yuehua | 2006 | Earthquake Research in China2006，20，3： | 3 |
| 5 | Application of fuzzy clustering method to determining sub-fault planes of earthquake from aftershocks sequence显示文摘Earthquake rupture process generally involves several faults activities instead of a single fault.A new method using both fuzzy clustering and principal component analysis makes it possible to reconstruct three dimensional structure of involved faults in earthquake if the aftershocks around the active fault planes distribute uniformly.When seismic events are given,the optimal faults structures can be determined by our new method.Each of sub-fault planes is fully characterized by its central location,length,width,strike and dip.The resolution determines the number of fault segments needed to describe the earthquake catalog.The higher the resolution,the finer the structure of the reconstructed fault segments.The new method successfully reconstructs the fault segments using synthetic earthquake catalogs.By taking the 28 June 1992 Landers earthquake occured in southern California as an example,the reconstructed fault segments are consistent with the faults already known on geological maps or blind faults that appeared quite frequently in longer-term catalogs. | Fuchang Wang Yongge Wan Huirong Cao Zhitong Jin Qingqing Ren | 2012 | Earthquake Science2012，25，2： | 1 |
| 6 | Co-seismic fault geometry and slip distribution of the 26 December 2004, giant Sumatra–Andaman earthquake constrained by GPS, coral reef, and remote sensing data显示文摘We analyze co-seismic displacement field of the 26 December 2004, giant Sumatra–Andaman earthquake derived from Global Position System observations,geological vertical measurement of coral head, and pivot line observed through remote sensing. Using the co-seismic displacement field and AK135 spherical layered Earth model, we invert co-seismic slip distribution along the seismic fault. We also search the best fault geometry model to fit the observed data. Assuming that the dip angle linearly increases in downward direction, the postfit residual variation of the inversed geometry model with dip angles linearly changing along fault strike are plotted. The geometry model with local minimum misfits is the one with dip angle linearly increasing along strike from 4.3oin top southernmost patch to 4.5oin top northernmost path and dip angle linearly increased. By using the fault shape and geodetic co-seismic data, we estimate the slip distribution on the curved fault. Our result shows that the earthquake ruptured *200-km width down to a depth of about 60 km.0.5–12.5 m of thrust slip is resolved with the largest slip centered around the central section of the rupture zone78N–108N in latitude. The estimated seismic moment is8.2 9 1022 N m, which is larger than estimation from the centroid moment magnitude(4.0 9 1022 N m), and smaller than estimation from normal-mode oscillation data modeling(1.0 9 1023 N m). | Yongge Wan Zheng-kang Shen Min Wang Yuehua Zeng Jichao Huang Xiang Li Huawei Cui Xiwei Gao | 2015 | Earthquake Science2015，28，3： | 1 |
| 7 | Present Tectonic Stress Field in the Capital Region of China Inverted from Focal Mechanisms of Small and Strong Earthquakes显示文摘A dense seismic network was installed in the capital region of China in recent years,which makes it possible to resolve the focal mechanisms of small earthquakes. We gathered large earthquake focal mechanisms from the last fifty years and moderate or small earthquake focal mechanisms from between 2002 and 2004,and calculated the present tectonic stress field of the capital region by the grid search method, which weighs different sized earthquakes and can improve the accuracy of the stress field inversion. The analysis of inversion results of different sub-regions shows that the azinuth of the maximum principal compressive stress axis is NE43°- 86° in the Beijing-Zhangjiakou-Datong area,NE38°-86° in the Tangshan area,and NE79°- 81° in the Xingtai area. Inversion results of this paper are similar to previous results,which proves the correctness of the approach. As revealed by the results,the stress field of the capital region is characterized by overall consistency and sub-regional differences. This study provides reference for earthquake mechanism explanation and geodynamics research. | Huang Jichao Wan Yongge | 2015 | Earthquake Research in China2015，29，4： | 1 |
| 8 | On the Consistency of Large Earthquake Moment and Strain Rate Inferred from GPS Data in North China显示文摘The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula (1974) translates the smoothed strain rates in North China into geodetic moment rates. In North China, the ratio of seismic moment released to moment accumulated from GPS measurement is 60.6% in NS direction, 68.9% in EW direction, and 104.1% in NE shear direction. The near unit ratio points to the reliability of GPS measurements there. The combination of historical seismicity and GPS measurement offers a powerful attack on earthquake hazard. | Wan Yongge He Zhende Shen Zhengkang Gan Weijun Wang Aijun | 2005 | Earthquake Research in China2005，19，3： | 0 |
| 9 | 2008年汶川地震产生的库仑应力演化及其对2013年M_W6.6芦山地震的延迟触发显示文摘2008年5月12日Mw7.9汶川地震近5年之后,在距汶川地表破裂南端西南约45kin处,发生了4月20日Mw6.6芦山地震(Hanetal,2014;Zhangetal,2014;图1)。这两个事件如此近的空间和时间距离表明后面的事件是前面事件的余震,换句话说,前面的事件对后面事件发生所起的作用比长期构造加载作用大。前人对这个问题的研究有不同的看法。 | Yanzhao Wang Fan Wang Min Wang Zhengkang Shen Yongge Wan 万永魁 | 2015 | 世界地震译丛2015，46，5： | 0 |
| 10 | Study on the Triggering Effect of the October, 2005 Pakistan M_W7.6 Earthquake on Its Aftershocks显示文摘The influences upon aftershocks of Coulomb failure stress change (CFSC) generated by the main-shock of the October 8, 2005, Pakistan earthquake are calculated and analyzed. The following factors are included in the calculation: (1) the difference between the pore fluid pressure and the medium elastic constant in the fault plane area and those of its surrounding medium; (2) the tectonic stress direction of the seismic source area; (3) the aftershock failure mechanism of aftershocks is calculated by stacking the tectonic stress with the stress change generated by the main-shock. Our study, which includes many factors, fits fairly well with the aftershock distribution. It indicates that most of the aftershocks were triggered by the Pakistan main-shock that occurred on October 8, 2005. | Wan Yongge Shen Zhengkang Shang Dan | 2007 | Earthquake Research in China2007，21，1： | 0 |
| 11 | 基于震源机制解数据反演构造应力张量的网格搜索法及其在中国、越南和老挝边界地区的应用显示文摘应力场在地球动力学研究方面起着至关重要的作用。本研究给出了由震源机制解数据反演应力张量及其置信范围的网格搜索法。我们使用人工合成震源机制解数据对该算法进行了测试,人工合成的震源机制解数据由拉张型、挤压型和走滑型3种类型应力场生成,并对生成的震源机制解数据添加不同水平的噪声。测试结果表明,相对于传统方法,本研究给出的方法反演出的应力场精度得到显著提高。本文算法主要有以下3个优点:(1)由精细的网格搜索获得应力张量的全局最优解,搜索网格为1°×1°×1°×0.01,避免了搜索结果落入局部最小值;(2)在反演应力张量的过程中,本方法可以考虑震源机制解数据精度的不同,并赋予不同的权重;(3)由F检验给出应力张量结果的置信范围。我们将该方法应用于中国、越南和老挝的边界地区,获得该地区应力场的主压应力方向为SSE—NNW,主张应力方向为NEE—SWW。应力比R为0.6,这意味着应力张量的特征值接近等差数列。该地区应力场与奠边—琅勃拉邦弧形断裂的左旋走滑性质一致,所得结果对该地区的地质动力学过程研究有一定的帮助。 | Yongge Wan Shuzhong Sheng Jichao Huang Xiang Li Xin Chen 杨帆 | 2017 | 世界地震译丛2017，48，2： | 0 |
| 12 | An Overview of the Study on Stress Magnitude显示文摘Crustal stress field holds an important position in geodynamics research, such as in plate motion simulations, uplift of the Qinghai-Xizang (Tibet) Plateau and earthquake preparation and occurrence. However, most of the crustal stress studies emphasize particularly on the determination of stress direction, with little study being done on stress magnitude at present. After reviewing ideas on a stress magnitude study from geological, geophysical and various other aspects, a method to estimate the stress magnitude in the source region according to the deflection of stress direction before and after large earthquakes and the stress drop tensor of earthquake rupture has been developed. The proposed method can also be supplemented by the average apparent stress before and after large earthquakes. The stress direction deflection before and after large earthquakes can be inverted by massive focal mechanisms of foreshocks and aftershocks and the stress drop field generated by the seismic source can be calculated by the detailed distribution of the earthquakes rupture. The mathematical relationship can then be constructed between the stress drop field, where its magnitude and direction are known and the stress tensor before and after large earthquakes, where its direction is known but magnitude is unknown, thereby obtaining the stress magnitude. The average apparent stress before and after large earthquakes can be obtained by using the catalog of broadband radiated energy and seismic moment tensor of foreshocks and aftershocks and the different responses to stress drops. This relationship leads to another estimation of stress magnitude before a large earthquake. The stress magnitude and its error are constrained by combining the two methods, which provide new constraints for the geodynamics study. | Sheng Shuzhong Wan Yongge | 2009 | Earthquake Research in China2009，23，2： | 0 |
| 13 | Stress value in 2003 Dayao Ms6.1 earthquake source region显示文摘The M S 6.2 Dayao,Yunnan,earthquake occurred on July 21,2003,followed by a major M S 6.1 earthquake about 88 days later in the same region.Hypocenters of the two earthquakes are almost in the same place.Based on the P wave first motion polarities of the two aftershock sequences recorded by temporary stations,we have studied the stress field in the aftershock zone and obtained the two stress field directions in Dayao region using the new version of PKU Grid Test Software provided by Chunquan Yu.Assuming that the rotation of the stress field is caused by the second main shock,we estimated the crustal stress value in the focal region by using the stress value calculation method proposed by Yongge Wan.The estimated maximum,intermediate and minimum principal stresses are 166.3 MPa,158.7 MPa and 151 MPa,respectively,before the second main shock.The normal and shear stresses projected on the fault plane of the second main shock before it occurred are 157.3 MPa,7.4 MPa,and are 158.8 MPa,0.2 MPa after it occurred,respectively.The perturbed input parameters experiments attest the stability of the solution.The result shows that the preseismic shear stress is larger than the post-seismic one,and their difference corresponds to the stress drop approximately.The estimated compressive stress level is very high,but the differential stress is low.The result is helpful for friction coefficient estimation,plate motion simulation and related studies. | Xiaofeng Xu Yongge Wan Huilin Wang | 2011 | Earthquake Science2011，24，4： | 0 |
| 14 | Co-seismic Slip Distribution of the 2001 Kokoxili Earthquake Inverted by the GPS Data显示文摘The authors analyze co_seismic displacement field derived from the Global Position System (GPS) observations collected before and after the 2001 Kokoxili earthquake, western China. Using the co_seismic displacement data, and constrained with surface rupture data, they invert co_seismic slip distribution along the seismic fault. Their result shows that the earthquake ruptured the upper crust down to a depth of 13.1~22km (at 70% certainty), with its optimal estimate at 16.5km. A 2~3m left_lateral strike slip is resolved between the Sun Lake segment and the west end of the main rupture zone, although surface rupture has not been observed there. The surface rupture of this earthquake is ended at the Sun Lake to the west, but left_lateral slip of 1.5~2.0m seems to exist beyond the east end of surface rupture observed from field geology. Seismic moment release estimated using GPS and surface rupture measurement is 6.0×10 20 N·m, which is in good agreement with the result obtained from seismic wave inversion. | Wan Yongge Shen Zhengkang He Zhende Wang Min Chen Jie Zhang Zusheng Wang Qingliang Gan Weijun | 2005 | Earthquake Research in China2005，19，4： | 0 |
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