Bedrock erosion and relief production in the northern Flinders Ranges,Australia

Cosmogenic ¹⁰Be concentrations in exposed bedrock surfaces and alluvial sediment in the northern Flinders Ranges reveal surprisingly high erosion rates for a supposedly ancient and stable landscape. Bedrock erosion rates increase with decreasing elevation in the Yudnamutana Catchment, from summit surfaces (13·96 ± 1·29 and 14·38 ± 1·40 m Myr^?1), to hillslopes (17·61 ± 2·21 to 29·24 ± 4·38 m Myr^?1), to valley bottoms (53·19 ± 7·26 to 227·95 ± 21·39 m Myr^?1), indicating late Quaternary increases to topographic relief. Minimum cliff retreat rates (9·30 ± 3·60 to 24·54 ± 8·53 m Myr^?1) indicate that even the most resistant parts of cliff faces have undergone significant late Quaternary erosion. However, erosion rates from visibly weathered and varnished tors protruding from steep bedrock hillslopes (4·17 ± 0·42 to 14·00 ± 1·97 m Myr^?1) indicate that bedrock may locally weather at rates equivalent to, or even slower than, summit surfaces. ¹⁰Be concentrations in contemporary alluvial sediment indicate catchment‐averaged erosion at a rate dominated by more rapid erosion (22·79 ± 2·78 m Myr^?1), consistent with an average rate from individual hillslope point measurements. Late Cenozoic relief production in the Yudnamutana Catchment resulted from (1) tectonic uplift at rates of 30–160 m Myr^?1 due to range‐front reverse faulting, which maintained steep river gradients and uplifted summit surfaces, and (2) climate change, which episodically increased both in situ bedrock weathering rates and frequency–magnitude distributions of large magnitude floods, leading to increased incision rates. These results provide quantitative evidence that the Australian landscape is, in places, considerably more dynamic than commonly perceived. Copyright © 2006 John Wiley & Sons, Ltd.     

Geomorphic and cosmogenic nuclide constraints on escarpment evolution in an intraplate setting,Darling Escarpment,Western Australia

The ～900 km long Darling Scarp in Western Australia is one of the most prominent linear topographic features on Earth. Despite the presence of over‐steepened reaches in all westerly flowing streams crossing the scarp, and significant seismic activity within 100 km of the scarp, there is no historical seismicity and no reported evidence for Quaternary tectonic displacements on the underlying Darling Fault. Consequently, it is unclear whether the scarp is a rapidly evolving landform responding to recent tectonic and/or climatic forcing or a more slowly evolving landform. In order to quantify late Quaternary rates of erosion and scarp relief processes, we obtained measurements of the cosmic‐ray produced nuclide beryllium‐10 (¹⁰Be) from outcropping bedrock surfaces along the scarp summit and face, in valley floors, and at stream knickpoints. Erosion rates of bedrock outcrops along the scarp summit surface range from 0·5 to 4·0 m Myr^?1. These are in the same range as erosion rates of 2·1 to 3·6 m Myr^?1 on the scarp face and similar to river incision rates of 2·6 to 11·0 m Myr^?1 from valley floor bedrock straths, indicating that the Darling Scarp is a slowly eroding ‘steady state’ landform, without any significant contemporary relief production over the last several 100 kyr and possibly several million years. Knickpoint retreat rates determined from ¹⁰Be concentrations at the bases of two knickpoints on small streams incised into the scarp are 36 and 46 m Myr^?1. If these erosion rates were sustained over longer timescales, then associated knickpoints may have initiated in the mid‐Tertiary to early Neogene, consistent with early‐mid Tertiary marginal uplift. Ongoing maintenance of stream disequilibrium longitudinal profiles is consistent with slow, regional base level lowering associated with recently proposed continental‐scale tilting, as opposed to differential uplift along discrete faults. Cosmogenic ¹⁰Be analysis provides a useful tool for interpreting the palaeoseismic history of intraplate near‐fault landforms over 10⁵ to 10⁶ years. Copyright © 2010 John Wiley & Sons, Ltd.     

26Al/10Be ratios reveal the source of river sediments in the Kimberley,NW Australia

We use cosmogenic ¹⁰Be and ²⁶Al in both bedrock and fluvial sediments to investigate controls on erosion rates and sediment supply to river basins at the regional scale in the Kimberley, NW Australia. The area is characterised by lithologically controlled morphologies such as cuestas, isolated mesas and extensive plateaus made of slightly dipping, extensively jointed sandstones. All sampled bedrock surfaces at plateau tops, ridgelines, and in the broader floodplain of major rivers over the region show similar slow lowering rates between 0.17 and 4.88 m.Myr^-1, with a mean value of 1.0 ± 0.6 m.Myr^-1 (n=15), whilst two bedrock samples collected directly within river-beds record rates that are one to two orders of magnitude higher (14.4 ± 1.5 and 20.9 ± 2.5 m.Myr^-1, respectively). Bedrock ²⁶Al/¹⁰Be ratios are all compatible with simple, continuous sub-aerial exposure histories. Modern river sediment yield lower ¹⁰Be and ²⁶Al concentrations, apparent ¹⁰Be basin-wide denudation rates ranging between 1.8 and 7.7 m.Myr^-1, with a median value of 2.6 m.Myr^-1, more than double the magnitude of bedrock erosion rates. ²⁶Al/¹⁰Be ratios of the sediment samples are lower than those obtained for bedrock samples. We propose that these depleted ²⁶Al/¹⁰Be ratios can largely be explained by the supply of sediment to river basins from the slab fragmentation and chemical weathering of channel gorge walls and plateau escarpments that result in diluting the cosmogenic nuclide concentration in river sediments measured at the basin outlets. The results of a mass-balance model suggest that ~60–90% of river sediment in the Kimberley results from the breakdown and chemical weathering of retreating vertical sandstone rock-walls in contrast to sediment generated by bedrock weathering and erosion on the plateau tops. This study emphasises the value of analysing two or more isotopes in basin-scale studies using cosmogenic nuclides, especially in slowly eroding post-orogenic settings. © 2019 John Wiley & Sons, Ltd.     

汶川M_W7.9地震起始破裂断层几何结构

本文收集使用紫坪铺水库台网记录到的汶川地震主震P波波形资料,利用P波反投影叠加法获取了2008年5月12日汶川M_W7.9地震起始破裂的时空演化过程.通过分析本次大地震起始破裂阶段(0～1s)破裂点在三维空间内的分布特征,确定了本次大地震起始破裂位置及起始破裂断层几何结构模型.得到以下结果:汶川地震起始破裂点位于31.013±0.002°N、103.392±0.002°E,震源深度为8.2±0.4km,发震时刻为2008年5月12日14∶27∶58.80±0.4.汶川地震起始破裂的最佳断层面走向为NE48°,倾向NW35°,起始阶段破裂的深度范围为地下7.5～9km.     

Doppler effect of the rupture process of the great MW7.9 Wenchuan earthquake

In this study we performed a classical spectrum analysis of seismic waveforms recorded at far field stations of the great M_W7.9 Wenchuan earthquake to observe the shifts of the corner frequency with azimuth due to the Doppler effect. Our results show that this damaging great earthquake had a dominating rupture propagation direction of 64.0°. The equivalent radius of the fault rupture surface was estimated to be 33 km, yielding the rupture area of about 3 500 km². Thus the length of the rupture fault surface is about 230 km if the depth (or width) extent is 15 km. The computer program developed in this study can quickly provide the information about the source of a future large (damaging) earthquake, which could be very useful for predicting aftershocks and planning the rescue operations.

     

基于区域地震波形的2017年新疆精河MS6.6地震破裂方向性及发震构造研究

2017年8月9日的新疆精河MS6.6地震是近年来天山北缘发生的最大地震,震中位于由多条逆冲断层组成的库松木契克断裂带内.由于震源较深、构造形变复杂、区域地震台站相对稀疏,仅根据震源机制解、余震分布和InSAR观测结果等难以直接判定发震构造.本文针对倾滑型地震发展了一种基于区域地震波形的破裂方向性测定方法,利用余震作为参考地震进行路径校正,根据主震和参考地震的波形时移差和Pn-Pg到时差分别确定主震在水平方向和深度方向的破裂尺度,进而推断同震破裂的延展方向和延伸尺度.本文在反演了主震的点源参数后,应用新发展的方法测定了地震的破裂方向性.点源反演结果显示,精河地震是一个发生在中地壳的高角度逆冲地震,矩震级约6.2,质心深度21km,震源持续时间5.5s,两个双力偶节面分别为102°/45°/106°(NP1)和259°/47°/74°(NP2).破裂方向性分析结果显示,地震的破裂面为南倾的NP1节面,地震沿着破裂起始点向西南方向、向下破裂,总破裂长度约11.5km,其中,沿深度的破裂范围约7km,沿水平的破裂范围约9km,平均破裂速度约2.1km·s-1.综合区域地质资料、卫星影像等判定本次地震的发震断层为精河南断层,地震可能只破裂了断层的下段(17~25km),并未破出地表.     

Spatio-temporal rupture process of the 2008 great Wenchuan earthquake

Focal mechanism and dynamic rupture process of the Wenchaun M _s8.0 earthquake in Sichuan province on 12 May 2008 were obtained by inverting long period seismic data from the Global Seismic Network (GSN), and characteristics of the co-seismic displacement field near the fault were quantitatively analyzed based on the inverted results to investigate the mechanism causing disaster. A finite fault model with given focal mechanism and vertical components of the long period P-waves from 21 stations with evenly azimuthal coverage were adopted in the inversion. From the inverted results as well as aftershock distribution, the causative fault of the great Wenchuan earthquake was confirmed to be a fault of strike 225°/dip 39°/rake 120°, indicating that the earthquake was mainly a thrust event with right-lateral strike-slip component. The released scalar seismic moment was estimated to be about 9.4×10²⁰-2.0×10²¹ Nm, yielding moment magnitude of M _w7.9–8.1. The great Wenchuan earthquake occurred on a fault more than 300 km long, and had a complicated rupture process of about 90 s duration time. The slip distribution was highly inhomogeneous with the average slip of about 2.4 m. Four slip-patches broke the ground surface. Two of them were underneath the regions of Wenchuan-Yingxiu and Beichuan, respectively, with the first being around the hypocenter (rupture initiation point), where the largest slip was about 7.3 m, and the second being underneath Beichuan and extending to Pingwu, where the largest slip was about 5.6 m. The other two slip-patches had smaller sizes, one having the maximum slip of 1.8 m and lying underneath the north of Kangding, and the other having the maximum slip of 0.7 m and lying underneath the northeast of Qingchuan. Average and maximum stress drops over the whole fault plane were estimated to be 18 MPa and 53 MPa, respectively. In addition, the co-seismic displacement field near the fault was analyzed. The results indicate that the features of the co-seismic displacement field were coincident with those of the intensity distribution in the meizoseismal area, implying that the large-scale, large-amplitude and surface-broken thrust dislocation should be responsible for the serious disaster in the near fault area. Supported by the National Basic Research Program of China (Grant No. 2004CB418404-4) and the National Natural Science Foundation of China (Grant Nos. 40574025 and 40874026)     

High-precision relocation of the aftershock sequence of the January 8, 2022, MS6.9 Menyuan earthquake

The 2022 Menyuan M_S6.9 earthquake, which occurred on January 8, is the most destructive earthquake to occur near the Lenglongling (LLL) fault since the 2016 Menyuan M_S6.4 earthquake. We relocated the mainshock and aftershocks with phase arrival time observations for three days after the mainshock from the Qinghai Seismic Network using the double-difference method. The total length and width of the aftershock sequence are approximately 32 km and 5 km, respectively, and the aftershocks are mainly concentrated at a depth of 7–12 km. The relocated sequence can be divided into 18 km west and 13 km east segments with a boundary approximately 5 km east of the mainshock, where aftershocks are sparse. The east and west fault structures revealed by aftershock locations differ significantly. The west fault strikes EW and inclines to the south at a 71º–90º angle, whereas the east fault strikes 133º and has a smaller dip angle. Elastic strain accumulates at conjunctions of faults with different slip rates where it is prone to large earthquakes. Based on surface traces of faults, the distribution of relocated earthquake sequence and surface ruptures, the mainshock was determined to have occurred at the conjunction of the Tuolaishan (TLS) fault and LLL fault, and the west and east segments of the aftershock sequence were on the TLS fault and LLL fault, respectively. Aftershocks migrate in the early and late stages of the earthquake sequence. In the first 1.5 h after the mainshock, aftershocks expand westward from the mainshock. In the late stage, seismicity on the northeast side of the east fault is higher than that in other regions. The migration rate of the west segment of the aftershock sequence is approximately 4.5 km/decade and the afterslip may exist in the source region.     

InSAR数据约束的2021年5月21日云南漾濞MS6.4地震发震构造研究

运用Sentinel-1A卫星数据和D-InSAR技术,获取2021-05-21云南漾濞M_S6.4地震的同震形变场。结果显示,漾濞地震同震形变场长轴近NW展布升降轨形变场符号相反,视线向最大沉降量和抬升量为0.1 m。InSAR同震形变场反演的滑动分布主要集中在沿走向2～12 km,倾向1～9 km的范围内,最大滑动量0.35 m,发震断层长9.8 km、宽4 km,滑动量主要集中在地下3～6 km范围内,滑动角-146.7°。同震位移场及滑动分布模型反映本次地震为发震断层的右旋走滑事件,地震破裂未达到地表。断层模型反演结果显示,矩震级为M_W6.1,发震断层以北西走向右旋走滑运动为主,初步认为本次M_W6.1地震发震断裂可能是一条NW向的维西—乔后断裂西侧的隐伏次生断裂。     

Surface rupture zone of the 1303 Hongtong M=8 earthquake, Shanxi Province

Based on the latest displacement of Huoshan piedmont fault, Mianshan west-side fault and Taigu fault obtained from the beginning of 1990‘s up to the present, the characteristics of distribution and displacement of surface rupture zone of the 1303 Hongtong M = 8 earthquake, Shanxi Province are synthesized and discussed in the paper. If Taigu fault, Mianshan west-side fault and Huoshan piedmont fault were contemporarily active during the 1303 Hongtong M = 8 earthquake, the surface rupture zone would be 160 km long and could be divided into 3 segments, that is, the 50-km-long Huoshan piedmont fault segment, 35-km-long Mianshan west-side fault segment and 70-km-long Taigu fault segment, respectively. Among them, there exist 4 km and 8 km step regions. The surface rupture zone exhibits right-lateral features. The displacements of northern and central segments are respectively 6～7 m and the southern segment has the maximum displacement of 10 m. The single basin-boundary fault of Shanxi fault-depression system usually corresponds to M ≈ 7 earthquake, while this great earthquake (M = 8) broke through the obstacle between two basins. It shows that the surface rupture scale of great earthquake is changeable.     

Fault plane parameters of Sanhe-Pinggu M8 earthquake in 1679 determined using present-day small earthquakes

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.     

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

An earthquake of M _S=7.4 occurred in Mani, Xizang (Tibet), China on November 8, 1997. The moment tensor of this earthquake was inverted using the long period body waveform data from China Digital Seismograph Network (CDSN). The apparent source time functions (ASTFs) were retrieved from P and S waves, respectively, using the deconvolution technique in frequency domain, and the tempo-spatial rupture process on the fault plane was imaged by inverting the azimuth dependent ASTFs from different stations. The result of the moment tensor inversion indicates that the P and T axes of earthquake-generating stress field were nearly horizontal, with the P axis in the NNE direction (29°), the T axis in the SEE direction (122°) and that the NEE-SWW striking nodal plane and NNW-SSE striking nodal plane are mainly left-lateral and right-lateral strike-slip, respectively; that this earthquake had a scalar seismic moment of 3.4×10²⁰ N·m, and a moment magnitude of M _W=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 ASTFs were retrieved by deconvoving the synthetic seismograms from the observed seismograms. The ASTFs retrieved from the P and S waves of different stations identically suggested that this earthquake was of a simple time history, whose ASTF can be approximated with a sine function with the half period of about 10 s. Inverting the azimuth dependent ASTFs from P and S waveforms led to the image showing the tempo-spatial distribution of the rupture on the fault plane. From the "remembering" snap-shots, the rupture initiated at the western end of the fault, and then propagated eastward and downward, indicating an overall unilateral rupture. However, the slip distribution is non-uniform, being made up of three sub-areas, one in the western end, about 10 km deep ("western area"); another about 55 km away from the western end and about 35 km deep ("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 rupturing appeared quite complex, with the slip occurring in different position at different time, and the earthquake being of the characteristics of "healing pulse". Another point we have to stress is that the locations in which the rupture initiated and terminated were not where the main rupture took place. Eventually, the static slip distribution was calculated, 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 about 70 km eastern to the epicenter; from the aftershock distribution, however, the aftershocks were very sparse in the west to the epicenter while densely clustered in the east to the epicenter. It indicated that the Mani M _S=7.9 earthquake was resulted from the nearly eastward extension of the NEE-SWW to nearly E-W striking fault in the northwestern Tibetan plateau. Contribution No. 99FE2016, Institute of Geophysics, China Seismological Bureau. This work is supported by SSTCC Climb Project 95-S-05 and NSFDYS 49725410.     

Frequency-domain array technique analysis for the rupture duration time and geometrical characteristics of the 2001 Kunlun Mountain Pass earthquake

In this paper, we briefly describe the principle of tracking energy radiation sources of large earthquakes using fre- quency-domain far-field array technique, present general steps of tracking energy radiation sources, and take the 2001 Kunlun Mountain Pass earthquake as an example to analyze key factors for setting parameters while pro- cessing data. Using broadband waveform data from a seismic array in Ethiopia and Kenya (EK Array), we obtain that the rupture initiation point of the 2001 Kunlun Mountain Pass earthquake is located in the east of Buka Daban Peak (35.92°N, 91.70°E), and the rupture duration time is less than 160 s, the rupture length about 520 km, with 180 km in the west of the initiation point and 340 km in the east, respectively. The western segment of the earth- quake fault bends towards southwest near Buka Daban Peak, which is in concordance with the surface rupture trace. The eastern segment apparently bends towards northeast near Xidatan, which is in agreement with the strike of Xidatan fault, but 30 km away from Xidatan fault. In addition, the results imply that the western segment of the earthquake fault appears erect while the eastern segment appears to be gradually dipping southwards.     

Coseismic deformation of the 2021 MW7.4 Maduo earthquake from joint inversion of InSAR,GPS, and teleseismic data

The M_W7.4 Maduo earthquake occurred on 22 May 2021 at 02:04 CST with a large-expansion surface rupture. This earthquake was located in the Bayan Har block at the eastern Tibetan Plateau, where eight earthquakes of M_S >7.0 have occurred in the past 25 years. Here, we combined interferometric synthetic aperture radar, GPS, and teleseismic data to study the coseismic slip distribution, fault geometry, and dynamic source rupture process of the Maduo earthquake. We found that the overall coseismic deformation field of the Maduo earthquake is distributed in the NWW-SEE direction along 285°. There was slight bending at the western end and two branches at the eastern end. The maximum slip is located near the eastern bending area on the northern branch of the fault system. The rupture nucleated on the Jiangcuo fault and propagated approximately 160 km along-strike in both the NWW and SEE directions. The characteristic source rupture process of the Maduo earthquake is similar to that of the 2010 M_W6.8 Yushu earthquake, indicating that similar earthquakes with large-expansion surface ruptures and small shallow slip deficits can occur on both the internal fault and boundary fault of the Bayan Har block.     

Review of the source characteristics of the Great Sumatra–Andaman Islands earthquake of 2004

The December 26, 2004 Sumatra–Andaman Island earthquake, which ruptured the Sunda Trench subduction zone, is one of the three largest earthquakes to occur since global monitoring began in the 1890s. Its seismic moment was M ₀ = 1.00 × 10²³–1.15 × 10²³ Nm, corresponding to a moment-magnitude of M _w = 9.3. The rupture propagated from south to north, with the southerly part of fault rupturing at a speed of 2.8 km/s. Rupture propagation appears to have slowed in the northern section, possibly to ∼2.1 km/s, although published estimates have considerable scatter. The average slip is ∼5 m along a shallowly dipping (8°), N31°W striking thrust fault. The majority of slip and moment release appears to have been concentrated in the southern part of the rupture zone, where slip locally exceeded 30 m. Stress loading from this earthquake caused the section of the plate boundary immediately to the south to rupture in a second, somewhat smaller earthquake. This second earthquake occurred on March 28, 2005 and had a moment-magnitude of M _w = 8.5.     

2016年印尼苏门答腊岛海域MW7.8地震震源运动学特征

根据中国和全球地震台网记录的波形记录,采用W震相矩张量反演、反投影分析及有限断层模型反演方法,研究了2016年3月2日印尼7.8级地震破裂过程,分析讨论印尼地震震源运动学特征.结果表明：此地震为一次对称的双侧破裂走滑型事件,北北东─南南西向的断层节面（走向5°/倾角85°）为发震断层面.标量地震矩约6.19×10²⁰ Nm,矩震级为7.79,最大的滑动量约11 m,位于破裂起始点北东,沿着断层走向约30 km处.破裂平均速度2.0~2.2 km·s^-1,破裂持续时间35 s,破裂在5~25 s内释放的能量,约占总能量的97%.最终形成了总长度90 km左右的断层.印尼地震具有破裂持续时间短、破裂速度慢、高滑动能量带相对集中等显著特点.本研究对进一步增进海洋岩石圈地震的震源特性认识有重要参考意义.     

2022门源MS6.9地震地表破裂带震害特征调查

2022年1月8日,青海省海北藏族自治州门源县发生M_S6.9地震,震中位于青藏高原东北缘地区祁连—海原断裂带的冷龙岭断裂和托勒山断裂构造转换区域(37.77°N,101.26°E)。震后野外现场考察结果表明,此次地震形成的同震地表破裂带总长度约为26 km,整体走向NWW向,破裂性质以左旋走滑局部逆冲为主。断层错动造成的破坏形式以雁列式组合的张裂隙、张剪裂隙、挤压鼓包、断层陡坎等为主。其中,道河至硫磺沟段地表破裂最为强烈,规模大且连续性好,造成的震害最为显著,地表破裂规模向东、西两端逐渐衰减。破裂带穿过区域内多条河流,造成显著的冰面破裂变形,并沿河岸形成一系列的边坡崩塌、滚石等地质灾害。综合破裂带及震害规模分析,宏观震中位于道河至硫磺沟地区。     

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

We conducted moment tensor inversion and studied source rupture process for M _S=7.9 earthquake occurred in the border area of China, Russia and Mongolia on September 27 2003, by using digital teleseismic P-wave seismograms recorded by long-period seismograph stations of the global seismic network. Considering the aftershock distribution and the tectonic settings around the epicentral area, we propose that the M _S=7.9 earthquake occurred on a fault plane with the strike of 127°, the dip of 79° and the rake of 171°. The rupture process inversion result of M _S=7.9 earthquake shows that the total rupture duration is about 37 s, the scalar moment tensor is M ₀=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 M _S=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.     

2008年汶川8.0级地震发震断裂的滑动速率、复发周期和构造成因

2008年5.12汶川大地震发生在中国大陆南北地震带中段.由于龙门山断裂带历史上只发生过3次6～6¹/₂级强震,而且其晚第四纪构造活动速率很低,以至于对其潜在地震危险性认识不足.为什么在龙门山地区突发大地震,该地震具有哪些特征？其成因机制是什么？本文在地震地质科学考察的基础上,利用震前的GPS观测结果,试图对上述问题进行一些初步的思考和探讨.结果表明,5.12汶川大地震是龙门山断裂带的映秀—北川断裂突发错动的结果,地表上形成200多公里长的地表破裂带;灌县—江油断裂在地震中也发生了破裂,形成的地表破裂带长达60多公里.震前的GPS观测表明,横跨整个龙门山断裂带的滑动速率不超过～2 mm/yr,单条断裂的活动速率不超过～1 mm/yr,与地震地质研究结果和历史地震记录相一致.利用地震地质考察和地震波反演得到的最大同震位移可以获得相当于5.12汶川大地震的强震复发周期为2000～6000年.龙门山断裂带发育在破裂强度很大的变质杂岩体中,断裂带本身在剖面上呈“犁形”或“铲形”结构,有利于能量积累,形成破坏性巨大的地震.所以,5.12汶川大地震是一次低滑动速率、长复发周期和高破坏强度的巨大地震,是一种值得高度重视和深入研究的新的地震类型.     

智利M_W8.3地震与M_W8.8地震的震源过程及其引起的库仑应力特征

2015年9月17日6时54分32秒(北京时间)智利中部伊拉佩尔附近(震中31.57°S,71.67°W)发生了一次M_w8.3大地震,在此次地震震中以南约500 km处的马乌莱地区曾于2010年2月27日14时34分11秒发生过一次M_w8.8强震(震中36.12°S,72.90°W),两次地震余震分布区之间有约75 km的地震空区.本文利用远场体波与面波波形,基于有限断层模型,反演了这两次地震的震源破裂过程.结果显示这两次地震均为逆冲型大地震,2015年伊拉佩尔M_w8.3地震的平均滑动角度为107°,平均滑动量为2.43 m,平均破裂速度为1.82 km·s~(-1),标量地震矩为3.28×10~(21)Nm,95%的标量地震矩在104 s内得到了释放.最大滑动量约8 m,位于沿走向75 km,深度8 km处.2010年马乌莱M_w8.8地震的平均滑动角度为109°,平均滑动量为4.95 m,平均破裂速度1.90 km·s~(-1),标量地震矩为1.86×10~(22)Nm,95%的标量地震矩在121 s内得到了释放.最大滑动量约12.5 m,位于沿走向100 km,深度21 km处.2015年伊拉佩尔M_w8.3地震浅部更大的滑动量应该是其引起了较大海啸的一个原因.基于破裂滑动分布,我们计算了这两次地震引起的周边俯冲带上静态库仑应力变化,结果显示两次地震均显著增加了周边俯冲带上的库仑应力,2010年马乌莱地震使得2015.年伊拉佩尔地震震源区附近的库仑应力增加了(0.01~0.15)×10~5Pa,从应力积累的角度看,2010年马乌莱地震有利于2015年伊拉佩尔地震的发生,对后者的发生起到了促进作用.