Source rupture process inversion of the 2013 Lushan earthquake,China

The spatial and temporal slip distribution of the Lushan earthquake was estimated using teleseismic body wave data. To perform a stable inversion, we applied smoothing constraints and determined their optimal relative weights on the observed data using an optimized Akaike＇ s Bayesian Information Criterion （ABIC）. The inversion generated the source parameters. Strike, dip and slip were 218°, 39° and 100. 8° ,respectively. A seismic moment （M0） was 2. 1 × 10^20 Nm with a moment magnitude （Mw） of 6. 8, and a source duration was approximately 30 second. The rupture propagated along the dip direction, and the maximum slip occurred at the hypocenter. The maximum slip was approximately 2. 1 m, although this earthquake did not cause an apparent surface rupture. The energy was mainly released within 10 second. In addition, the Lushan earthquake was apparently related to the 2008 Wenchuan earthquake. However, the question of whether it was an aftershock of the Wenchuan earthquake requires further study.

Moment tensor inversion and source rupture process of the September 27, 2003 M_S=7.9 earthquake occurred in the border area of China, Russia and Mongolia

plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process inversion result of MS=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tensor is M0=0.97 × 1020 N·m. Rupture mainly occurred on the shallow area with 110 km long and 30 km wide, the location in which the rupture initiated is not where the main rupture took place, and the area with slip greater than 0.5 m basically lies within 35 km deep middle-crust under the earth surface. The maximum static slip is 3.6 m. There are two distinct areas with slip larger than 2.0 m. We noticed that when the rupture propagated towards northwest and closed to the area around the MS=7.3 hypocenter, the slip decreased rapidly, which may indicate that the rupture process was stopped by barriers. The consistence of spatial distribution of slip on the fault plane with the distribution of aftershocks also supports that the rupture is a heterogeneous process owing to the presence of barriers.

Rupture process of the January 8, 2022, Menyuan M 6.9 earthquake

After the occurrence of destructively strong earthquakes, rapid acquisition of the source rupture process can provide important reference information for post-earthquake disaster relief and aftershock trend determination.An M 6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. The epicenter is located in the seismic gap in the middle section of the Haiyuan fault belt. Such a typical strong earthquake was taken as an example to investigate the rupture process of strong earthquakes. Three days after the earthquake, the InSAR(Interferometric Synthetic Aperture Radar) coseismic deformation field was obtained by Sentinel radar, indicating that the surface ruptured obviously. The southern block of the earthquake faces towards the satellite about 95 cm along the LOS(line of sight) direction, and the northern block is away from the satellite by ~ 74 cm, consistent with the characteristic of left-lateral strike-slip motion. In this study, InSAR coseismic deformation data and farfield waveform data were used to jointly invert the earthquake rupture process, and a four-segment finite fault model was constructed by referring to the surface deformation. The inversion results show that the focal depth of the Menyuan earthquake is about 7 km, and the strike of the seismogenic fault is 89.0°, 104.0°, 119.0°and 131.0°from west to east, respectively. It is a high-dip left-lateral strike-slip earthquake event lasting about 14 s. The rupture propagation mode is a bilateral extension. The maximum slip along the fault is about 380 cm, and the seismic moment magnitude is 6.7. The surface rupture length is about 24 km, which is consistent with that measured in the field survey. The detailed seismic source model can provide basic data for the aftershock trend determination and seismic risk analysis of the adjacent active faults.

Inversion of near-field waveform data for earthquake source rupture process (I): Method and numerical test

A new inversion algorithm for simultaneously reconstructing the slip vectors and rupture times of a propagating finite fault is developed based on the recent progress in the nonlinear pro-gramming study. To check the validity of this new inversion algorithm, several numerical tests are conducted. The results show that this new source rupture process inversion algorithm is computa-tionally efficient and numerically stable, and depends less on the initial model compared with the two popular inversion methods, i.e. the linear matrix method and the global stochastic search method. Therefore, this new inversion algorithm is expected to be useful in inverting earthquake rupture processes.

Source rupture process of Lushan M_S7.0 earthquake, Sichuan,China and its tectonic implications

The source rupture process of the MS7.0 Lushan earthquake was here evaluated using 40 long-period P waveforms with even azimuth coverage of stations.Results reveal that the rupture process of the Lushan MS7.0 event to be simpler than that of the Wenchuan earthquake and also showed significant differences between the two rupture processes.The whole rupture process lasted 36 s and most of the moment was released within the first 13 s.The total released moment is 1.9×1019N m with MW=6.8.Rupture propagated upwards and bilaterally to both sides from the initial point,resulting in a large slip region of 40 km×30 km,with the maximum slip of 1.8 m,located above the initial point.No surface displacement was estimated around the epicenter,but displacement was observed about 20 km NE and SW directions of the epicenter.Both showed slips of less than 40 cm.The rupture suddenly stopped at 20 km NE of the initial point.This was consistent with the aftershock activity.This phenomenon indicates the existence of significant variation of the medium or tectonic structure,which may prevent the propagation of the rupture and aftershock activity.The earthquake risk of the left segment of Qianshan fault is worthy of attention.

Inversion of near-field waveform data for earthquake source rupture process(Ⅱ):Inversion of Chi Chi earthquake source,20 September,1999,Taiwan

The new inversion algorithm developed based on the recent progress in thenonlinear programming study by us is used to invert the earthquake source process of Chi Chiearthquake M_w7.6, 20 Semptember,1999, Taiwan. A curve fault model is constructed in our inversionto make the fault model close to the real rupturing fault to reduce the influence from thediscrepancy between the constructed fault model and the real rupturing fault. The results show that(1) the rupture process of the Chi Chi earthquake source lasted about 32 seconds and the mainfaulting occurred between 6th to 21st second after the start of the ruptures and the high slip areawere mainly located at the northern segment of the fault. (2) The slip was dominated by thrustfaulting. The average rake angle was 64.5°, which was very consistent with those inverted by USGS,Harvard and CWB (Central Weather Bureau of Taiwan). The amount of the moment inverted in this paperwas 7.76x10^(20) NM, which was a slightly bigger than those inverted by USGS and Harvard. (3) Aclear nucleation step existed in the source faulting process and it lasted about 6 seconds. Themoment release rate accelerated obviously at the end of the nucleation step. The faulting startedfrom the southern segment and mainly occurred at the northern segment after 10 seconds. At the endof this paper, we analyzed the reliability of the inversion result via comparing with the GPSobservations and discussed its scientific signification.

Tempo-spatial rupture process of the 1997Mani, Xizang(Tibet), China earthquake of Ms=7.9

An earthquake of Ms=7.4 occurred in Mani, Xizang (Tibet), China on November 8, 1997. The moment tensor ofthis earthquake was inverted using the long period body wave form data from China Digital Seismograph Network(CDSN). The apparent source time functions (AS TFs) were retrieved from P and S waves, respectively, using thedeconvolution technique in frequency domain, and the tempo-spatial rupture process on the fault plane was imagedby inverting the azimuth dependent AS TFs from different stations. The result of the moment tensor inversionindicates that the P and T axes of earthquake-generating stress field were nearly horizontal, with the P axis in theNNE direction (29), the T axis in the SEE direction (122) and that the NEE-SWW striking nodal plane andNNW-SSE striking nodal plane are mainly left-lateral and right-lateral strike-slip, respectively; that this earthquakehad a scalar seismic moment of 3.4xl02o N. .m, and a moment magnitude of Mw=7.6. Taking the aftershock distribution into account, we proposed that the earthquake rupture occurred in the fault plane with the strike of 250,the dip of 88 and the rake of 19. On the basis of the result of the moment tensor inversion, the theoretical seismograms were synthesized, and then the AS T Fs were retrieved by deconvoving the synthetic seismograms fromthe observed seismograms. The A S T Fs retrieved from the P and S waves of different stations identically suggestedthat this earthquake was of a simple time history, whose ASTF can be approximated with a sine function with thehalf period of about 10 s. Inverting the azimuth dependent A S T Fs from P and S waveforms led to the imageshowing the tempo-spatial distribution of the rupture on the fault plane. From the 'remembering' snap-shots, therupture initiated at the western end of the fault, and then propagated eastward and downward, indicating an overallunilateral rupture. However, the slip distribution is non-uniform, being made up of three sub-areas, one in thewestern end, about 10 km deep ('western area'), another about 55 kin away from the western end and about 35 Iondeep ('eastern area'), the third about 30 km away from the western end and around 40 km deep ('central area').The total rupture area was around 70 km long and 60 km wide. From the 'forgetting' snap-shots, the rupturingappeared quite complex, with the slip occurring in different position at different time, and the earthquake being ofthe characteristics of 'healing pulse'. Another point we have to stress is that the locations in which the ruptureinitiated and terminated were not where the main rupture took place. Eventually, the static slip distribution wascalculated, and the largest slip values of the three sub-areas were 956 cm, 743 cm and 1 060 cm, for the western.eastern and central areas, respectively. From the slip distribution, the rupture mainly distributed in the fault about70 km eastern to the epicenter; from the aftershock distribution. however, the aftershocks were very sparse in thewest to the epicenter while densely clustered in the east to the epicenter It indicated that the Maul Ms=7.9 earthquake was resulted from the nearly eastward extension of the NEE-SWW to nearly E-W striking fault in thenorthwestern Tibetan plateau.

Rupture process of the 2011 Tohoku earthquake from the joint inversion of teleseismic and GPS data

Teleseismic and GPS data were jointly inverted for the rupture process of the 2011 Tohoku earthquake. The inversion results show that it is a bilateral rupture event with an average rupture velocity less than 2.0 km/s along the fault strike direction. The source rupture process consists of three sub-events, the first oc- curred near the hypocenter and the rest two ruptured along the up-dip direction and broke the sea bed, causing a maximum slip of about 30 m. The large-scale sea bed breakage may account for the tremendous tsunami disaster which resulted in most of the death and missing in this mega earthquake.

Fast inversion of rupture process of the 14 April 2010 Yushu,Qinghai,earthquake

Four results of the rupture process of 14 April 2010 Yushu, Qinghai, earthquake, obtained by inverting the broadband seismic data of Global Seismographic Network （GSN） based on the inversion method of earthquake rupture process, were compared and discussed. It is found that the Yushu earthquake has several basic characteristics as follows： 1 There exist two principal sub-events which correspond to two slip-concentrated patches being located near the hypocenter and to the southeast of the epicenter. The rupture of the slip-concentrated patch to the southeast of the epicenter broke though the ground surface; 2 The peak slip and peak slip-rate are about 2.1 m and 1.1 m/s, respectively, indicating that the Yushu earthquake is an event with large slip-rate on the fault plane; 3 Overall the Yushu earthquake is a unilateral rupture event with the rupture mainly propagating southeastward. The strong focusing of the seismic energy in the southeast of the epicenter due to the ＂seismic Doppler effect＂ reasonably accounts for the tremendous damage in the Yushu city.

Preliminary result for the rupture process of Nov.13, 2017,Mw7.3 earthquake at Iran-Iraq border

At UTC 2017-11-12 18:18:17,an Mw7.3 earthquake occurred at the border between Iran and Iraq(location 34.886°N,45.941°E,depth 23 km according to USGS).We carried out focal mechanism and rupture process studies with the data from IRIS data center,using 26 far-field P-waveforms and 25 SH-waveforms with high S/N ratio and relatively even azimuth coverage(epicentral distance)in a point source model to invert for the focal mechanism solution;the result(Figure1)was used to construct a finite fault model for rupture process inversion(Yao and Ji,1997;Wang et al.,2008),resulting in a preliminary slip distribution of this earthquake(Figures 2-4).The calculated seismic moment is 1.1×1020 N·m,Mw=7.3.The maximum slip is about 700 cm.

Preliminary results for the rupture process of Jan.10, 2018, Mw7.6 earthquake at east of Great Swan Island, Honduras

At UTC 2018-01-10 02:51:31,an Mw7.6 earthquake occurred 44 km east of Great Swan Island,Honduras(location 17.469°N,83.520°W,depth 10 km,according to the United States Geological Survey).We carried out studies of the focal mechanism and rupture process of the earthquake,using seismic data from the IRIS data center.For the focal mechanism solution,a point source model was used to invert 26 far-field P-waveforms and 26 SHwaveforms with high S/N ratio and relatively even azimuth coverage(epicentral distance 30°<△<90°);then the result(Figure 1)was used to construct a finite fault model for rupture process inversion(Yao ZX and Ji C,1997;Wang WM et al.,2008),resulting in a preliminary model of the slip distribution of this earthquake(Figures 2–4).The calculated seismic moment is 2.41×10^20 N·m and the estimated earthquake magnitude Mw=7.5.The maximum slip is about 1900 cm.

Imaging the rupture process of the 10 January 2018 Mw7.5 Swan island, Honduras earthquake

The 10 January 2018 Mw7.5 Swan island,Honduras earthquake occurred on the Swan island fault,which is a transform plate boundary between the North American and Caribbean plates.Here we back-project the rupture process of the earthquake using dense seismic stations in Alaska,and find that the earthquake ruptured at least three faults(three stages)for a duration of~40 s.The rupture speed for the longest fault(stage 3)is as fast as 5 km/s,which is much faster than the local shear wave velocity of~4 km/s.Supershear rupture was incidentally observed on long and straight strike-slip faults.This study shows a supershear rupture that occured on a strike-slip fault with moderate length,implying that supershear rupture might commonly occur on large strike-slip earthquakes.The common occurrence of supershear rupture on strike-slip earthquakes will challenge present understanding of crack physics,as well as strong ground motion evaluation in earthquake engineering.

Estimation of the 2010 Mentawai tsunami earthquake rupture process from joint inversion of teleseismic and strong ground motion data

Joint inversion of teleseismic body-wave data and strong ground motion waveforms was applied to determine the rupture process of the 2010 Mentawai earthquake. To obtain stable solutions, smoothing and non-negative constraints were introduced. A total of 33 teleseismic stations and 5 strong ground motion stations supplied data. The teleseismic and strong ground motion data were separately windowed for 150 s and 250 s and bandpass filtered with frequencies of 0.001e1.0 Hz and 0.005e0.5 Hz, respectively. The finitefault model was established with length and width of 190 km and 70 km, and the initial seismic source parameters were set by referring to centroid moment tensor(CMT) solutions. Joint inversion results indicate that the focal mechanism of this earthquake is thrust fault type, and the strike, dip, and rake angles are generally in accordance with CMT results. The seismic moment was determined as 5.814 1020Nm(Mw7.8) and source duration was about 102 s, which is greater than those of other earthquakes of similar magnitude. The rupture nucleated near the hypocenter and then propagated along the strike direction to the northwest, with a maximum slip of 3.9 m. Large uncertainties regarding the amount of slip retrieved using different inversion methods still exist; however, the conclusion that the majority of slip occurred far from the islands at very shallow depths was found to be robust. The 2010 Mentawai earthquake was categorized as a tsunami earthquake because of the long rupture duration and the generation of a tsunami much larger than was expected for an earthquake of its magnitude.

Preliminary Study on the Correlation between Intensity Isoseismals and the Seismic Source Process of the Wenchuan Earthquake in Sichuan,China

The M_S8.0 Wenchuan earthquake in Sichuan caused heavy casualties and serious economic loss because of damage to engineering structures in high earthquake intensity regions. Earthquake intensity, especially in the near source region, as a macroscopic description of distribution of strong ground motions certain correlations with the earthquake source process, such as rupture directivity and the hanging-wall effect of the near-fault ground motions of this earthquake. In this article some qualitative analyses are carried out. The conclusion of this study may be useful for emergence response and rescue after earthquakes, when the strong ground motion recordings and the intensity distribution are not available immediately.

Source process of the 14 November 2001 western Kunlun Mountain M_S=8.1 earth-quake

Based on digital teleseismic P-wave seismograms recorded by 28 long-period seismograph stations of the global seismic network, source process of the November 14, 2001 western Kunlun Mountain MS=8.1 (MW=7.8) earth- quake is estimated by a new inversion method. The result shows that the earthquake is a very complex rupture event. The source rupture initiated at the hypocenter (35.95°N, 90.54°E, focal depth 10 km, by USGS NEIC), and propagated to the west at first. Then, in several minutes to a hundred minutes and over a large spatial range, several rupture growth points emerged in succession at the eastern end and in the central part of the finite fault. And then the source rupture propagated from these rupture growth points successively and, finally, stopped in the area within 50 km to the east of the centroid position (35.80°N, 92.91°E, focal depth 15 km, by Harvard CMT). The entire rupture lasted for 142 s, and the source process could be roughly separated into three stages: The first stage started at the 0 s and ended at the 52 s, lasting for 52 s and releasing approximately 24.4% of the total moment; The sec- ond stage started at the 55 s and ended at the 113 s, lasting for 58 s and releasing approximately 56.5% of the total moment; The third stage started at the 122 s and ended at the 142 s, lasting for 20 s and releasing approximately 19.1% of the total moment. The length of the ruptured fault plane is about 490 km. The maximum width of the ruptured fault plane is about 45 km. The rupture mainly occurred within 30 km in depth under the surface of the Earth. The average static slip in the underground rocky crust is about 1.2 m with the maximum static slip 3.6 m. The average static stress drop is about 5 MPa with the maximum static stress drop 18 MPa. The maximum static slip and the maximum stress drop occurred in an area within 50 km to the east of the centroid position.

Rupture behavior of the 2017 M_(W)6.6 Poso earthquake in Sulawesi,Indonesia

On May 29, 2017, the MW6.6 Poso earthquake occurred in Central Sulawesi, Indonesia, causing moderate damages. The mainshock rupture and primary aftershock cluster occurred in the active Palolo-Sausu tectonic zone, and some aftershocks also took place around the Tokararu fault. However, the rupture mechanism of this earthquake and its relation to regional tectonics are not clear. In this study, the rupture process of the Poso mainshock is estimated by finite-fault waveform inversion, which is constrained by teleseismic bodies and surface waves. The rupture propagates upward unilaterally in a southwest-dipping moderate-angle(~34°) normal fault beneath Tokorondo Mountains, with a notable~15% initial moment release at the first 4 s of the ~12 s rupture duration. The average and peak slip are0.5 m and 1.5 m, respectively. The rupture velocity is relatively slow(less than 2.5 km/s), and the Coulomb stress changes due to the mainshock are obtained using the inverted coseismic slip.

2023年12月18日甘肃积石山6.2级地震震源参数和破裂特征

2023年12月18日23时59分(北京时间)甘肃积石山发生6.2地震。中国地震局地球物理研究所在震后启动快速响应,组织相关领域研究人员对此次地震的震源参数、震源机制、破裂过程和地震辐射能量等进行了估计,余震序列进行了重定位,基于震源模型进行了震动图模拟、同震形变场模拟。结果表明,此次地震发生在拉脊山东侧,以逆冲机制为主,能量集中在前约8 s内释放;极震区震动烈度可能达Ⅷ度以上,可能的受灾范围近6 000 km~2;此次地震引起了显著的同震位移,最大水平向位移达到7.8 cm、垂直向位移达到15.8 cm。

区域地震记录揭示的2023年甘肃积石山6.2级地震震源破裂过程

基于有限断层模型反演方法,利用区域宽频带地震波形数据,反演了2023年12月18日甘肃临夏积石山6.2级地震的震源破裂过程,获得了积石山地震破裂滑动时空分布:此次地震是逆冲兼少量走滑型地震,破裂持续时间约为9 s,主体能量在前6 s释放,地震破裂主要沿断层走向向NW方向拓展,计算得到的标量地震矩为1.39×10^(18)N·m,相当于M_(W)6.02,破裂尺度约10 km左右,最大同震滑动量为35 cm。

2023年12月2日菲律宾棉兰老岛附近海域7.6级地震的快速产出参数

北京时间2023年12月2日22时37分在菲律宾棉兰老岛(Mindanao)东部海域发生7.6级地震。中国地震局地球物理研究所在震后启动快速响应,组织相关领域研究人员对此次地震的震源参数、震源机制、破裂过程和地震辐射能量等进行了估计,基于震源模型进行了震动图模拟、同震形变场模拟。结果表明,此次地震发生在菲律宾海板块与欧亚板块/巽他地块碰撞的俯冲带板片上,以逆冲机制为主,能量集中在前约40 s内释放,断层破裂最大滑动量达到7 m;震源辐射地震能量的效率偏低,慢度系数略低于全球平均水平,与同样矩震级大小的地震相比,震感不强烈;极震区震动烈度可能达Ⅸ度以上,可能的受灾范围近27000 km^(2);此次地震引起了显著的同震位移,最大水平向位移达到0.6 m、垂直向位移达到1.2 m。综合分析可知,此次地震不会产生大规模海啸。

利用远场记录反演2023年甘肃积石山M6.2地震破裂过程

2023年12月18日23时59分在甘肃临夏积石山发生了M6.2地震,地震发震断层推测为此前尚未充分认知的积石山东缘断裂。本文利用远场地震记录反演分析了2023年积石山M6.2地震的破裂过程。结果表明,地震破裂持续时间约8 s,主要破裂长度为20~25 km,宽度约25 km。在走向为164°的节面Ⅰ上,整个破裂过程释放的标量地震矩为1.46×10^(18)N·m,相当于矩震级MW6.05,最大同震滑动量约为0.25 m,估计矩心深度为9.5 km,破裂主要沿断层走向SSE向扩展;在走向为303°的节面Ⅱ上,释放的标量地震矩为1.38×10^(18)N·m,相当于矩震级MW6.03,最大同震滑动量约为0.19 m,矩心深度为11.1 km。破裂呈现双侧形态,主要沿SE方向,并存在NW向的拓展趋势。