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1.
The Maule, Chile, (Mw 8.8) earthquake on 27 February 2010 triggered deformation events over a broad area, allowing investigation of stress redistribution within the upper crust following a mega-thrust subduction event. We explore the role that the Maule earthquake may have played in triggering shallow earthquakes in northwestern Argentina and Chile. We investigate observed ground deformation associated with the Mw 6.2 (GCMT) Salta (1450 km from the Maule hypocenter, 9 h after the Maule earthquake), Mw 5.8 Catamarca (1400 km; nine days), Mw 5.1 Mendoza (350 km; between one to five days) earthquakes, as well as eight additional earthquakes without an observed geodetic signal. We use seismic and Interferometric Synthetic Aperture Radar (InSAR) observations to characterize earthquake location, magnitude and focal mechanism, and characterize how the non-stationary, spatially correlated noise present in the geodetic imagery affects the accuracy of our parameter estimates. The focal mechanisms for the far-field Salta and Catamarca earthquakes are broadly consistent with regional late Cenozoic fault kinematics. We infer that dynamic stresses due to the passage of seismic waves associated with the Maule earthquake likely brought the Salta and Catamarca regions closer to failure but that the involved faults may have already been at a relatively advanced stage of their seismic cycle. The near-field Mendoza earthquake geometry is consistent with triggering related to positive static Coulomb stress changes due to the Maule earthquake but is also aligned with the South America-Nazca shortening direction. None of the earthquakes considered in this study require that the Maule earthquake reactivated faults in a sense that is inconsistent with their long-term behavior.  相似文献   

2.
Seismicity of Gujarat   总被引：2，自引：2，他引：0  
Paper describes tectonics, earthquake monitoring, past and present seismicity, catalogue of earthquakes and estimated return periods of large earthquakes in Gujarat state, western India. The Gujarat region has three failed Mesozoic rifts of Kachchh, Cambay, and Narmada, with several active faults. Kachchh district of Gujarat is the only region outside Himalaya-Andaman belt that has high seismic hazard of magnitude 8 corresponding to zone V in the seismic zoning map of India. The other parts of Gujarat have seismic hazard of magnitude 6 or less. Kachchh region is considered seismically one of the most active intraplate regions of the World. It is known to have low seismicity but high hazard in view of occurrence of fewer smaller earthquakes of M????6 in a region having three devastating earthquakes that occurred during 1819 (M w7.8), 1956 (M w6.0) and 2001 (M w7.7). The second in order of seismic status is Narmada rift zone that experienced a severely damaging 1970 Bharuch earthquake of M5.4 at its western end and M????6 earthquakes further east in 1927 (Son earthquake), 1938 (Satpura earthquake) and 1997 (Jabalpur earthquake). The Saurashtra Peninsula south of Kachchh has experienced seismicity of magnitude less than 6.  相似文献   

3.
Paper describes triggered seismicity to 200?km distance and for a decade due to the 2001 M w7.7 Bhuj earthquake. The Kachchh region is seismically one of the most active intraplate regions of the World due to the occurrence of two large earthquakes 1819 (M w7.8) and 2001 (M w7.7). Though, it has high hazard but was known to have low seismicity in view of the occurrence of fewer smaller shocks. However, the status seems to have changed after 2001. Besides the strong aftershock activity for over a decade, seismicity has spread to nearby faults in Kachchh peninsula and at several places southward for 200?km distance in Saurashtra peninsula. Beyond the rupture zone of the 2001 Bhuj earthquake, more than 40 mainshocks of M w?~?3?C5 have occurred at 20 different locations, which is unusual. The increased seismicity is inferred to be caused by stress perturbation due to the 2001 Bhuj earthquake by viscoelastic process. In Saurashtra, over and above the viscoelastic stress increase, the transient stress increase by water table rise in monsoons seems to be affecting the timing of mainshocks and associated sequences of earthquakes.  相似文献   

4.
This paper presents a combination of seismic imaging, geomorphologic, and tectonic data and an interpretation of the M = 5.1 1980 Arudy earthquake sequence putting in relation the seismicity, the inherited faults, and the geomorphologic (Würm and postwürm) markers in this region of the Pyrenees. Since the anticlockwise rotation of the regional compression axis in Oligocene time, western Pyrenees are under a dextral regime and the resulting motion is accommodated along major inherited E–W dextral strike-slip faults. The Arudy aftershocks sequence is controlled by antecedent horsetail splay faults built at the boundary between two shallow Mesozoic crustal blocks most probably due to their differing rheology. This boundary has played the role of a seismic barrier stopping the E–W slip motion. The Arudy earthquake has reactivated the eastern segment of the main E–W strike-slip fault, while the post-seismic aftershocks correspond to local relaxation processes in normal tectonic behavior.  相似文献   

5.
Following the 1999 Mw 7.6 Chi-Chi earthquake, a large amount of seismicity occurred in the Nantou region of central Taiwan. Among the seismic activities, eight Mw ⩾ 5.8 earthquakes took place following the Chi-Chi earthquake, whereas only four earthquakes with comparable magnitudes took place from 1900 to 1998. Since the seismicity rate during the Chi-Chi postseismic period has never returned to the background level, such seismicity activation cannot simply be attributed to modified Omori’s Law decay. In this work, we attempted to associate seismic activities with stress evolution. Based on our work, it appears that the spatial distribution of the consequent seismicity can be associated with increasing coseismic stress. On the contrary, the stress changes imparted by the afterslip; lower crust–upper mantle viscoelastic relaxation; and sequent events resulted in a stress drop in most of the study region. Understanding seismogenic mechanisms in terms of stress evolution would be beneficial to seismic hazard mitigation.  相似文献   

6.
据中国地震台网测定，2021年5月21日21时48分在云南省大理州漾濞县发生MS6.4地震，及时查明此次地震的发震构造及震源破裂特征，可为认识该区孕震条件和判别未来强震危险性提供关键依据。采用双差定位方法对漾濞地震序列进行重新定位，得到3863次地震事件的精确震源位置。结果显示:漾濞地震序列整体呈北西—南东向分布，长约25 km；整体走向135°；MS6.4主震震中位置为25.688°N，99.877°E；震源深度约9.6 km。综合地震序列深度剖面和震源机制解结果可知，发震断层应为北西走向、整体向西南方向陡倾的右旋走滑断层，倾角具有自北西向南东逐渐变缓的趋势。进一步分析地震序列的时空演化过程发现，该地震具有典型的"前震-主震-余震型"地震序列活动特点，其破裂过程主要包括3个阶段。破裂成核阶段:首先在发震断层10~12 km深度处相对脆弱部位产生小尺度破裂，之后失稳加速破裂，发生MS5.6地震；主震破裂阶段:在构造应力场持续加载和周围小尺度破裂的共同影响下，促使浅部较高强度断层闭锁区破裂，形成MS6.4主震；尾端拉张破裂阶段:主震破裂向东南扩展过程中，在东南端形成与之呈马尾状斜交的、具有正断性质的次级破裂，并产生MS5.2余震。而且此次地震还在源区北东侧触发了北北东向的左旋走滑破裂。综合分析认为，漾濞地震是兰坪-思茅地块内部北西向草坪断裂在近南北向区域应力挤压作用下发生右旋走滑运动的结果，具有明显的新生断裂特征。近年来兰坪-思茅地块内部一系列中强地震的发生表明，青藏高原物质向东南持续挤出的过程中，遇到该地块的阻挡，正在导致地块内部早期断层贯通形成新的活动断裂。因此，川滇地块西南边界带上或相邻地块内部老断层的复活和新生断裂的产生是区域中强地震危险性分析评价中值得关注的重要课题，同时建议需重视未来该区中强地震进一步向东南和向北的迁移或扩展的可能性。   相似文献   

7.
An earthquake of Mw 5.1 occurred on March 14, 2005, in the seismically active Koyna–Warna region in western India, the site known for the largest reservoir triggered seismicity (RTS) in the world. For more than four decades, earthquakes with M  4.0 have occurred in this region at regular intervals. Impoundment of reservoirs and changes in lake levels can trigger earthquakes by two processes of stress modifications, namely direct loading effect of the reservoir and diffusion through various faults and fractures. In this paper we analysed the reservoir water level data at Koyna and Warna reservoirs prior to the occurrence of the March 14, 2005 earthquake, to explain the dominant mechanism behind its occurrence and its correlation with the observed coseismic changes. We conclude that the diffusion process, not the reservoir load effect, is the dominating mechanism triggering earthquakes in the region. The coseismic changes in deep well water levels sensitive to earth tides are found to be to the order of 1–12 cm.  相似文献   

8.
A temporal seismic network recorded local seismicity along a 130 km long segment of the transpressional dextral strike-slip Liquiñe-Ofqui fault zone (LOFZ) in southern Chile. Seventy five shallow crustal events with magnitudes up to Mw 3.8 and depths shallower than 25 km were observed in an 11-month period mainly occurring in different clusters. Those clusters are spatially related to the LOFZ, to the volcanoes Chaitén, Michinmahuida and Corcovado, and to active faulting on secondary faults. Further activity along the LOFZ is indicated by individual events located in direct vicinity of the surface expression of the LOFZ. Focal mechanisms were calculated using deviatoric moment tensor inversion of body wave amplitude spectra which mostly yield strike-slip mechanisms indicating a NE–SW direction of the P-axis for the LOFZ at this latitude. The seismic activity reveals the present-day activity of the fault zone. The recent Mw 6.2 event near Puerto Aysén, Southern Chile at 45.4°S on April 21, 2007 shows that the LOFZ is also capable of producing large magnitude earthquakes and therefore imposing significant seismic hazard to this region.  相似文献   

9.
In the paper we report the state-of-the-art of seismicity study in the Baikal rift system and the general results obtained. At present, the regional earthquake catalog for fifty years of the permanent instrumental observations consists of over 185,000 events. The spatial distribution of the epicenters, which either gather along well-delineated belts or in discrete swarms is considered in detail for different areas of the rift system. At the same time, the hypocenters are poorly constrained making it difficult to identify the fault geometry. Clustered events like aftershock sequences or earthquake swarms are typical patterns in the region; moreover, aftershocks of M ⩾ 4.7 earthquakes make up a quarter of the whole catalog. The maximum magnitude of earthquakes recorded instrumentally is MLH7.6 for a strike-slip event in the NE part of the Baikal rift system and MLH6.8 for a normal fault earthquake in the central part of the rift system (Lake Baikal basin). Predominant movement type is normal faulting on NE striking faults with a left lateral strike-slip component on W–E planes. In conclusion, some shortcomings of the seismic network and data processing are pointed out.  相似文献   

10.
Like the tsunamis that accompanied the 2010 Maule (Chile) and the 2004 Sumatra-Andaman and 2005 Nias earthquakes, the tsunamis associated with the Tōhoku, Japan (Mw 9.0), earthquake of 11 March 2011 may owe more to slip on superficial faults on the sea floor than to the megathrust itself. The pattern of shallow aftershocks during the 24 h immediately following the main shock suggests that the crucial structures include faults in the upper plate, in the accretionary wedge landwards of the trench and on the outer rise. Seafloor geodetic observation could thus usefully contribute routinely to local hazard preparedness.  相似文献   

11.
Three large earthquakes (Mw>4.5) were triggered within 5 min, 85 km west of a Mw 6.5 earthquake in the South Iceland Seismic Zone (SISZ). We report on surface effects of these triggered earthquakes, which include fresh rupture, widespread rockfall, disrupted rockslides and block slides. Field data confirm that the earthquakes occurred along N-striking right-lateral strike-slip faults. Field data also support the conclusion from modeling of InSAR data that deformation from the second triggered event was more significant than for the other two. A major hydrological effect was the draining of water through an open fissure on a lake bed, lowering the lake level by greater than 4 m. Field relationships suggest that a component of aseismic slip could have been facilitated by water draining into the fault zone.  相似文献   

12.
Koyna-Warna Region (KWR) is one of the known sites for reservoir triggered seismicity. The continued triggered seismicity over the five decades is restricted to a region of about 600–700 sq. km, which provides a unique opportunity to monitor geophysical anomalies likely to be associated with seismicity of the region. Present study confers temporal gravity changes recorded by gPhone and GRACE satellite and interprets observed changes in conjunction with seismological, geodetic (cGPS) observations and groundwater level measurements. GRACE data suggest that seasonal vertical deformation due to hydrological loading is ～ 2 cm, which corroborates with continuous GPS observations. Seasonal hydrological loading of the region, which is in a phase of reservoir loading, might be influencing the critically stressed KWR leading to the seasonal seismicity of the region. The gPhone gravity data distinctly show co-seismic gravity signals for eight earthquakes of Mw > 2 and gravity anomalies show positive correlation on a logarithmic scale with earthquake released energy. To investigate the cause of gravity changes, an estimate is made for 14th April 2012 earthquake for Mw 4.8 using fault dislocation model. The recorded gravity changes of 189 μGal by gPhone located at a distance of 28 km from the hypocentre is much more than the estimate of ～0.1 μGal calculated for Mw 4.8 Koyna earthquake. Therefore, it is inferred that co-seismic gravity signals for eight earthquakes are primarily caused due to redistribution of mass at shallow depth.  相似文献   

13.
The Mw 7.7 earthquake that struck SE Pakistan on 24 September 2013 at 11.29.48 UTC was a sinistral strike-slip event on a branch of the Ornach-Nal-Chaman fault system which hereabouts separates the Eurasian Plate from the Indian Plate. Although the focus was at a depth of 15 km and 400 km inland the earthquake was accompanied by the emergence of an island off the Makran coast and the generation of a tsunami with a peak amplitude of 27 cm at Muscat (Oman) and 20 cm at Chah Bahar (Iran). At DART marine buoy 23228 in the Indian Ocean 500 km to the south a series of seismic Rayleigh waves about 4 min after the main shock was followed 54 min later by a tsunami with a peak amplitude of 1 cm. The Rayleigh series is here attributed to seafloor vibration during accelerated subduction of the Arabian Plate beneath the Eurasian Plate, and the tsunami to the development or reactivation of one or more reverse faults on the seaward portion of the Makran imbricate fan. As in the 2010.2.27 Mw 8.8 Maule (Chile), the 2004.12.26 Mw 9.2 Sumatra–Andaman, the 2005.3.28 Mw 8.7 Nias (Indonesia) and the 2011.3.11 Mw 9.0 Tohoku (Japan) earthquakes, the link between tsunami generation and slip on the megathrust is thus very indirect, to the detriment of attempts to mitigate coastal hazards using teleseismic data when nearshore seafloor monitoring would probably prove more effective.  相似文献   

14.
The Tarutung Basin is located at a right step-over in the northern central segment of the dextral strike-slip Sumatran Fault System (SFS). Details of the fault structure along the Tarutung Basin are derived from the relocations of seismicity as well as from focal mechanism and structural geology. The seismicity distribution derived by a 3D inversion for hypocenter relocation is clustered according to a fault-like seismicity distribution. The seismicity is relocated with a double-difference technique (HYPODD) involving the waveform cross-correlations. We used 46,904 and 3191 arrival differences obtained from catalogue data and cross-correlation analysis, respectively. Focal mechanisms of events were analyzed by applying a grid search method (HASH code). Although there is no significant shift of the hypocenters (10.8 m in average) and centroids (167 m in average), the application of the double difference relocation sharpens the earthquake distribution. The earthquake lineation reflects the fault system, the extensional duplex fault system, and the negative flower structure within the Tarutung Basin. The focal mechanisms of events at the edge of the basin are dominantly of strike-slip type representing the dextral strike-slip Sumatran Fault System. The almost north–south striking normal fault events along extensional zones beneath the basin correlate with the maximum principal stress direction which is the direction of the Indo-Australian plate motion. The extensional zones form an en-echelon pattern indicated by the presence of strike-slip faults striking NE–SW to NW–SE events. The detailed characteristics of the fault system derived from the seismological study are also corroborated by structural geology at the surface.  相似文献   

15.
Two contemporary earthquakes originating in the central Himalayan arc and its foredeep (Sikkim earthquake of 18.09.2011, Mw 6.9, h: 10–60 (?) km and Bihar-Nepal earthquake of 20.08.1988, Mw 6.8, h: 57 km) are commonly associated with transverse lineaments/faults traversing the region. Such lineaments/faults form active seismic blocks defining promontories for the advancing Indian Craton. These actually produce conjugate shear faulting pattern suggestive of pervasive crustal interplay deep inside the mountains. Focal mechanism solutions allow inferring that large part of the current convergence across the central Himalayan arc is accommodated by lateral slip. Similar slip also continues unabated in the densely populated foredeep for distances up to several tens of kilometers south of the Main Boundary Thrust (MBT).  相似文献   

16.
In this study, the seismicity rate changes that can represent an earthquake precursor were investigated along the Sagaing Fault Zone (SFZ), Central Myanmar, using the Z value technique. After statistical improvement of the existing seismicity data (the instrumental earthquake records) by removal of the foreshocks and aftershocks and man-made seismicity changes and standardization of the reported magnitude scales, 3574 earthquake events with a M w ≥ 4.2 reported during 1977–2015 were found to directly represent the seismotectonic activities of the SFZ. To find the characteristic parameters specifically suitable for the SFZ, seven known events of M w ≥ 6.0 earthquakes were recognized and used for retrospective tests. As a result, utilizing the conditions of 25 fixed earthquake events considered (N) and a 2-year time window (T w), a significantly high Z value was found to precede most of the M w ≥ 6.0 earthquakes. Therefore, to evaluate the prospective areas of upcoming earthquakes, these conditions (N = 25 and T w = 2) were applied with the most up-to-date seismicity data of 2010–2015. The results illustrate that the vicinity of Myitkyina and Naypyidaw (Z = 4.2–5.1) cities might be subject to strong or major earthquakes in the future.  相似文献   

17.
The Longquan–Shan fault and the Huya fault are two major neighboring faults of the Longmen–Shan fault zone where the 12 May 2008 Wenchuan earthquake (Mw 7.9) occurred. To study the influence of the Wenchuan event on these two active faults, we calculate changes of Coulomb stress on the Longquan–Shan fault and the Huya fault caused by the Wenchuan mainshock. Our results indicate that the Coulomb stress in the northern section (Zone A) of the Longquan–Shan fault is increased by 0.07–0.10 bars, that in the middle section (Zone B) by 0.04–0.11 bars, and that in the southern section (Zone C) shows almost no change. For the Huya fault, the Coulomb stress is decreased by 0.01–0.03 bars in the northern section (Zone A), 0.10–0.35 bars in the middle section (Zone B), and nearly 0.5 bars in the southern section (Zone C). The epicenter distribution of small earthquakes (ML ⩾ 1.5) on the Longquan–Shan fault and the Huya fault after the Wenchuan earthquake is consistent with the distribution of the Coulomb stress change. This implies that the Wenchuan earthquake may have triggered small events on the Longquan–Shan fault, but inhibited those on the Huya fault. We then use the rate/state friction law to calculate the occurrence probability of future earthquakes in the study region for the next decade. They include the distribution of b-values, magnitude of completeness (Mc), the background seismicity rate, a value of Aσn and the duration for the transient effect (ta) in the study region. We also estimate the earthquake occurrence probabilities on the neighboring faults after the Wenchuan earthquake. Our results show that, the occurrence probability of future earthquakes in the Longquan–Shan has a slight increase, being 7% for M ⩾ 5.0 shocks during the next decade, but the earthquake probability in the Huya region is reduced obviously, being 5–20%, 7–26% and 3–9% for M ⩾ 5.0 shocks during the next decade in sections A, B and C of the Huya fault, respectively.  相似文献   

18.
文章以地质地貌与地震遗迹野外调查获得的第一手资料为基础,重点介绍了实皆断裂的活动习性、2012年地震产生的建筑物破坏与地震地表破裂带特征.实皆断裂是一条规模宏大,以右旋走滑为主的全新世活动断裂,其水平滑动速率为18～20 mm/a.历史上沿实皆断裂曾发生10余次7级以上强震,迄今保留有1839年曼德勒因瓦M 8、193...  相似文献   

19.
湘东-赣西NNE向走滑断裂与地震、地热关系   总被引：4，自引：0，他引：4  
该文重点研究了湘东、赣西地区ＮＮＥ向活动走滑断裂系与地震和温泉分布之间的密切联系。结果表明：①研究区地震和温泉主要集中在３条ＮＮＥ向主走滑断裂带及及伴生的Ｐ、Ｐ’断裂带;②高温热泉或强震震中区的基本构造样式为走滑断层左行、左阶雁列带和拉分盆地构造;③陆壳结构分层特征是影响该区地震作用强度的一个重要因素。  相似文献   

20.
This report summarizes the seismicity in Switzerland and surrounding regions in the years 2015 and 2016. In 2015, the Swiss Seismological Service detected and located 735 earthquakes in the region under consideration. With a total of 20 earthquakes of magnitude ML ≥ 2.5, the seismic activity of potentially felt events in 2015 was close to the average of 23 earthquakes over the previous 40 years. Seismic activity was above average in 2016 with 872 located earthquakes of which 31 events had ML ≥ 2.5. The strongest event in the analyzed period was the ML 4.1 Salgesch earthquake, which occurred northeast of Sierre (VS) in October 2016. The event was felt in large parts of Switzerland and had a maximum intensity of V. Derived focal mechanisms and relative hypocenter relocations of aftershocks image a SSE dipping reverse fault, which likely also hosted an ML 3.9 earthquake in 2003. Another remarkable earthquake sequence in the Valais occurred close to Sion with four felt events (ML 2.7–3.2) in 2015/16. We associate this sequence with a system of WNW-ESE striking fault segments north of the Rhône valley. Similarities with a sequence in 2011, which was located about 10 km to the NE, suggest the existence of an en-echelon system of basement faults accommodating dextral slip along the Rhône-Simplon line in this area. Another exceptional earthquake sequence occurred close to Singen (Germany) in November 2016. Relocated hypocenters and focal mechanisms image a SW dipping transtensional fault segment, which is likely associated with a branch of the Hegau-Bodensee Graben. On the western boundary of this graben, micro-earthquakes close to Schlattingen (TG) in 2015/16 are possibly related to a NE dipping branch of the Neuhausen Fault. Other cases of earthquakes felt by the public during 2015/16 include earthquakes in the region of Biel, Vallorcine, Solothurn, and Savognin.  相似文献   

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