Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling

Saikia, Chandan K.; Woods, Bradley B.; Thio, Hong Kie

doi:10.1007/978-3-0348-8262-0_9

Cited by 4 publications

(6 citation statements)

References 29 publications

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“…Short period Rayleigh wave (Rg) is an important index [23] of shallow seismicity, because Rayleigh wave is only well developed when the epicentral distance is large enough. An intraplate earthquake is usually deeper than 5 km, so it is difficult to see Rg wave.…”

Section: Methodsmentioning

confidence: 99%

“…He used the differential time between Pg and sPg to measure focal depths of a number of earthquakes. Besides this, there are many related stduies on determining the focal depth using local depth phase [16][17][18][19][20][21][22][23][24][25]. In brief, the method of determining the focal depth with depth phase has broad application and this method is very useful especially when the station distribution is spare.…”

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confidence: 99%

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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: Methodsmentioning

confidence: 99%

mentioning

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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“…There are other depth phases, however, that are present in regional records that can also be used. In particular, the regional depth phases sPg, sPmP, and sPn, with their reference phases Pg, PmP, and Pn, respectively, are often clearly observable on regional records (e.g., Kings, 1979;Helmberger and Engen, 1980;Zonno and Kind, 1984;Langston, 1987Langston, , 1996Helmberger, 1991, 1993;Bock, 1993;Ebel, 1995;Bock et al, 1996;Zhu and Helmberger, 1997;Saikia, 2000;Saikia et al, 2001;Bent and Perry, 2002;Uski et al, 2003). (Note: Other candidate depth phases, such as pPg, are not generally observed at regional distances.)…”

Section: Introductionmentioning

confidence: 98%

Focal Depths for Small to Moderate Earthquakes (mN >=2.8) in Western Quebec, Southern Ontario, and Northern New York

Atkinson

2006

Bulletin of the Seismological Society of America

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Regional depth phase modeling is a useful technique to constrain earthquake focal depths for events within sparse networks. We demonstrate how regional depth phases can be used to obtain focal depths for hundreds of earthquakes with m N Ն2.8 that occurred from 1980 to 2004 in southern Ontario, western Quebec, and northern New York State. We discuss the development of regional depth phases with distance, their use in focal depth determinations by matching waveforms to synthetics, and possible sources of error. In general, focal depths can be determined to within about 3 km when there is at least one record at regional distances with clearly identifiable depth phases such as sPmP or sPg.In southwestern Ontario and northern New York, focal depths range from 2 to 15 km. In areas of western Quebec and along the Ottawa River valley in Ontario, focal depths range from 2 to 25 km. More than half of the earthquakes in a cluster of activity near Maniwaki in western Quebec are deeper than 20 km. All earthquakes deeper than 20 km occurred north of about 45.3Њ N.There is an intriguing tendency for earthquake depths to cluster near 8 km, 12 km, 15 km, and 22 km. Another interesting observation is that there are several earthquake pairs or small groups with very similar epicenters but quite different depths. The most active regions, in western Quebec and along the Ottawa River valley, tend to exhibit a relatively wide range of focal depths along broad zones that trend roughly northwest, suggesting that seismicity is occurring along diffuse northwest-trending faults throughout the crust. The wide range of focal depths may indicate the potential for a larger maximum scale of fault rupture and serve as a contemporary marker of locations where large events have occurred in the recent geologic past.

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“…Distribution of focal depth is essential for understanding stress regime at the depth where earthquake was located, regional seismicity and seismic hazards [3][4][5][6] ; it plays a particularly important role in relating seismicity to geologic structure and delineating active faults [7] . Reliably determined focal depth is also useful for establishing accurate epicentral location and origin time [8] .…”

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confidence: 99%

“…Since there is a strong trade-off between origin time and depth, especially for shallow-focus earthquake, error in depth determination is serious when local or regional stations nearby the source are unavailable. When the P-wave inversion is not convergent in focal depth, the time separation between depth phase sP (or pP) and its reference phase P is used to constrain focal depth by teleseismic seismograms modeling [3,[6][7][8][9][10] . Depth analysis is usually based on a generic global model, which does not consider the region-specific upper crust, and due to poor azimuthal coverage of seismic stations, thus the error in focal depth is significant even for large events (M w >5) [11] .…”

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confidence: 99%

Focal depths for moderate-sized aftershocks of the Wenchuan M S8.0 earthquake and their implications

Zhang

et al. 2008

Sci. China Ser. D-Earth Sci.

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Sliding-window cross-correlation method is firstly adopted to identify sPn phase, and to constrain focal depth from regional seismograms, by measuring the time separation between sPn and Pn phases. We present the focal depths of the 17 moderate-sized aftershocks (M S ≥5.0) of the Wenchuan M S 8.0 earthquake, using the data recorded by the regional seismic broadband networks of Shaanxi, Qinghai, Gansu, Yunnan and Sichuan. Our results show focal depths of aftershocks range from 8 to 20 km, and tend to cluster at two average depths, separate at 32.5°N, i.e., 11 km to the south and 17 km to the north, indicating that these aftershocks are origin of upper-to-middle crust. Combined with other results, we suggest that the Longmenshan fault is not a through-going crustal fault and the Pingwu-Qingchuan fault may be not the northward extension of the Longmenshan thrust fault.Wenchuan M S 8.0 earthquake, aftershocks, sPn phaseThe Wenchuan M S 8.0 earthquake is the largest intraplate earthquake in china in the latest 30 years, after the M S 8.1 Kunlunshan earthquake. Up to now, more than ten thousands of aftershocks were triggered and still continuously occurred. Among them, more than 39 aftershocks with magnitude greater than 5.0 occurred along the Longmenshan thrust belt, which provide us an opportunity to delineate the depth extension of the Longmenshan fault, and to address the problems whether the Longmenshan fault is a crustal extend fault suggested by deep seismic sounding data [1,2] , and the Pingwu-Qingchuan fault is the northern extension of the Longmenshan fault. Focal depth is one of the critical earthquake source parameters. Distribution of focal depth is essential for understanding stress regime at the depth where earthquake was located, regional seismicity and seismic hazards [3][4][5][6] ; it plays a particularly important role in relating seismicity to geologic structure and delineating active faults [7] . Reliably determined focal depth is also useful for establishing accurate epicentral location and origin time [8] .However, in source parameters, focal depth is difficult to be determined and sometimes not well constrained. In the routine location determination, focal depth is mainly constrained by modeling or inversion of teleseismic first arrival of P wave. Since there is a strong trade-off between origin time and depth, especially for shallow-focus earthquake, error in depth determination is serious when local or regional stations nearby the source are unavailable. When the P-wave inversion is not convergent in focal depth, the time separation between depth phase sP (or pP) and its reference phase P is used to constrain focal depth by teleseismic seismograms modeling [3,[6][7][8][9][10] . Depth analysis is usually based on a generic global model, which does not consider the region-specific upper crust, and due to poor azimuthal coverage of seismic stations, thus the error in focal depth is significant even for large events (M w >5) [11] . Many institutions often use a fixed value for those events with fo...

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Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling

Cited by 4 publications

References 29 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

Focal Depths for Small to Moderate Earthquakes (mN >=2.8) in Western Quebec, Southern Ontario, and Northern New York

Focal depths for moderate-sized aftershocks of the Wenchuan M S8.0 earthquake and their implications

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