Shear-wave splitting in a critical crust

Crampin, Stuart; Chastin, Sebastien; Gao, Yuan

doi:10.1016/j.jappgeo.2003.01.001

Cited by 49 publications

(8 citation statements)

References 23 publications

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“…Of course, the increase of stress near the surface caused by deep rupture is not necessarily large enough to generate an earthquake. However the crustal rocks in this region may have been in critical state close to failure, it was possible that a stress increase of 0.6 MPa could initiate a fresh fault [37].…”

Section: Conclusion and Discussionmentioning

confidence: 99%

A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone

Luo

Zeng

et al. 2010

Sci. China Earth Sci.

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Previous studies show that mature faults are filled with fault gouge in the shallow part and thus cannot accumulate enough strain energy for earthquakes. Therefore most earthquakes are deeper than 5 km, except those events occurring on new faults or in intact rocks. From field observation, Wenchuan earthquake is found to rupture the free surface about 200 km, but the rupture may extend underground much further from teleseismic body waves inversion and aftershocks distribution. In the northeastern end of the rupture zone, deep rupture may induce stress increase near the free surface, and trigger shallow earthquakes. An M s 5.7 aftershock occurred at Qingchuan, northeast end of Wenchuan earthquake fault on July 24, 2008, featuring thrust mechanism with a 3 km source centroid depth. The shallow focal depth is confirmed with the sPL phase recorded at station L0205. As Rayleigh wave is well only developed for source depth less than 1/5 of epicentral distance, the observed large amplitude of Rg at a distance of 15 km implied depth of 3 km or less. Dozens of aftershocks' sPL waveforms are also analyzed to confirm the source depths less than 3 km. On the other hand, no surface ruptures are found by geological survey or InSAR studies. It is strongly suggested that these aftershock sequences initiate fresh rupture in intact rocks triggered by stress increase from the deep co-seismic rupture of the Wenchuan mainshock.Wenchuan earthquake, shallow earthquake, focal depth, wave modeling Citation:Luo Y, Ni S D, Zeng X F, et al. A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone.On May 12, 2008, an M s 8.0 earthquake occurred at Wenchuan, Sichuan Province, and caused heavy economic loss and casualties. Dozens of strong aftershocks with magnitude ≥5.0 occurred along the Longmenshan faults in the following months. The depth and focal mechanism of the aftershock sequence provided a good constraint on mainshock fault and regional stress field. Focal depth is an important parameter to study regional seismicity and seismic hazard, and also plays a particularly important role in understanding the relationship between seismicity and geological structure. Depths of most intraplate earthquakes are between 5 and 25 km [1][2][3][4]. When depth is larger than 25 km, it is not very easy to accumulate strain because of ductile deformation in the lower crust. When depth is less than 5 km, mature faults are filled with soft fault gouge in the upper part; thus, it is difficult to accumulate enough strain. Recent studies show that the depths of Wenchuan earthquake aftershocks are mostly in the range of 5-20 km [5][6][7][8][9][10]. But in many regions, especially inside an old stable intraplate such as southwest part of Australia (Merkering) and North America, nearsurface stress measurements in the area show relatively high deviatoric stress. Because of strong strength in cold and old

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Section: Conclusion and Discussionmentioning

confidence: 99%

A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone

Luo

Zeng

et al. 2010

Sci. China Earth Sci.

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“…The consistency between the fast orientations and the direction of the maximum horizontal compression suggests that NW-SE oriented extensional cracks in the upper crust are mostly responsible for the observed anisotropy. Such a mechanism is commonly involved to explain crustal anisotropy in areas dominated by compressional tectonics (Crampin, 1981;1994 (Crampin et al, 2003). This mechanism implies a high pore pressure in the upper crust at the stations with two-layer anisotropy.…”

Section: Longmenshan Block and Adjacent Areasmentioning

confidence: 99%

Crustal anisotropy and ductile flow beneath the eastern Tibetan Plateau and adjacent areas

Kong

Liu

et al. 2016

Earth and Planetary Science Letters

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Crustal anisotropy beneath 71 broadband seismic stations situated at the eastern Tibetan Plateau and the Sichuan Basin is investigated based on the sinusoidal moveout of P-to-S conversions from the Moho and an intracrustal discontinuity. Significant crustal anisotropy is pervasively detected beneath the study area with an average splitting time of 0.39±0.18 s. The resulting fast orientations are mostly parallel to the major shear zones in the Songpan-Ganzi Terrane, and can be explained by fluid-filled fractures, favoring the model of rigid block motion with deformations concentrated on the block boundaries. In the vicinity of the Xianshuihe-Xiaojiang Fault Zone in the southern Songpan-Ganzi Terrane, our results, when combined with previously revealed high crustal Poisson's ratio in the area, support the existence of mid/lower crustal flow. The Longmenshan Fault Zone and adjacent areas are dominated by strike-orthogonal fast orientations, which are consistent with alignments of cracks associated with compressional stress between the Plateau and the Sichuan Basin. The observations suggest that

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“…c T 1 and the alert (after Rahimi Tabar et al 2007;Mokhtari et al 2007b) It has long been suspected that changes in shear wave splitting would monitor temporal changes of micro-crack geometry caused by changes of stress before earthquakes (Crampin 1978;Crampin et al 1984). This methodology has been used elsewhere, for example, in Iceland (Crampin et al 2003;Crampin and Gao 2006). Therefore, by gradual increase in know-how within the NCEP, this methodology will also be examined at the test site.…”

Section: Seismicmentioning

confidence: 99%

“…There are many examples in the literature where water level changes have been associated with earthquakes, either as precursors or as co-seismic and post-seismic events (Roeloffs 1988;Contadakis and Asteriadis 2001;Koizumi et al 2005;Kumpel 1992;Wang 1984;Crampin et al 2003). For example, about 3 months before the Longling earthquakes, the water level at a well at Xiaguan, Yunnan Province, began to lower by centimeters (Rikitake 1982).…”

Section: Water Level Changesmentioning

confidence: 99%

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Earthquake prediction activities and Damavand earthquake precursor test site in Iran

Mokhtari

2009

Nat Hazards

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Iran has long been known as one of the most seismically active areas of the world, and it frequently suffers destructive and catastrophic earthquakes that cause heavy loss of human life and widespread damage. The Alborz region in the northern part of Iran is an active EW trending mountain belt of 100 km wide and 600 km long. The Alborz range is bounded by the Talesh Mountains to the west and the Kopet Dagh Mountains to the east and consists of several sedimentary and volcanic layers of Cambrian to Eocene ages that were deformed during the late Cenozoic collision. Several active faults affect the central Alborz. The main active faults are the North Tehran and Mosha faults. The Mosha fault is one of the major active faults in the central Alborz as shown by its strong historical seismicity and its clear morphological signature. Situated in the vicinity of Tehran city, this 150-km-long N100°E trending fault represents an important potential seismic source. For earthquake monitoring and possible future prediction/precursory purposes, a test site has been established in the Alborz mountain region. The proximity to the capital of Iran with its high population density, low frequency but high magnitude earthquake occurrence, and active faults with their historical earthquake events have been considered as the main criteria for this selection. In addition, within the test site, there are hot springs and deep water wells that can be used for physico-chemical and radon gas analysis for earthquake precursory studies. The present activities include magnetic measurements; application of methodology for identification of seismogenic nodes for earthquakes of M C 6.0 in the Alborz region developed by International Institute of Earthquake Prediction Theory and Mathematical Geophysics, IIEPT RAS, Russian Academy of Science, Moscow (IIEPT&MG RAS); a feasibility study using a dense seismic network for identification of future locations of seismic monitoring stations and application of short-term prediction of medium-and large-size earthquakes is based on Markov and extended self-similarity analysis of seismic data. The establishment of the test site is ongoing, and the methodology has been selected based on the IASPEI evaluation report on the most important precursors with installation of (i) a local dense seismic network consisting of 25 short-period seismometers, (ii) a GPS network consisting of eight instruments with 70 stations, (iii) M. Mokhtari (magnetic network with four instruments, and (iv) radon gas and a physico-chemical study on the springs and deep water wells.

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Shear-wave splitting in a critical crust

Cited by 49 publications

References 23 publications

A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone

A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone

Crustal anisotropy and ductile flow beneath the eastern Tibetan Plateau and adjacent areas

Earthquake prediction activities and Damavand earthquake precursor test site in Iran

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