scholarly journals Mapping the <i>b</i>-values along the Longmenshan fault zone before and after the 12 May 2008, Wenchuan, China, <i>M<sub>S</sub></i> 8.0 earthquake

2008 ◽  
Vol 8 (6) ◽  
pp. 1375-1385 ◽  
Author(s):  
Y. Z. Zhao ◽  
Z. L. Wu
Keyword(s):  
Fault Zone ◽  
High Stress ◽  
B Value ◽  
Slip Distribution ◽  
Longmenshan Fault Zone ◽  
Magnitude Distribution ◽  
The North ◽  
Significant Difference ◽  
Before And After ◽  
Longmenshan Fault

Abstract. The b-value in the Gutenberg-Richter frequency-magnitude distribution, which is assumed to be related to stress heterogeneity or asperities, was mapped along the Longmenshan fault zone which accommodated the 12 May 2008, Wenchuan, MS 8.0 earthquake. Spatial distributions of b-value before and after the Wenchuan earthquake, respectively, were compared with the slip distribution of the mainshock. It is shown that the mainshock rupture nucleated near to, but not within, the high-stress (low b-value) asperity in the south part of the Longmenshan fault, propagating north-eastward to the relatively low stress (high b-value) region. Due to the significant difference between the rupture process results from different sources, the comparison between slip distribution and pre-seismic b-value distribution leads to only conclusion of the rule-of-thumb. The temporal change of b-value before the mainshock shows a weak trend of decreasing, being hard to be used as an indicator of the approaching of the mainshock. Distribution of b-values for the aftershocks relates the termination of the mainshock rupture to the harder patch along the Longmenshan fault to the north.

scholarly journals Seismic Structure of Local Crustal Earthquakes beneath the Zipingpu Reservoir of Longmenshan Fault Zone

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Haiou Li ◽  
Xiwei Xu ◽  
Wentao Ma ◽  
Ronghua Xie ◽  
Jingli Yuan ◽  
...  
Keyword(s):  
Fault Zone ◽  
Three Dimensional ◽  
P Wave ◽  
The Tibetan Plateau ◽  
Seismic Structure ◽  
Infiltration Depth ◽  
Low Velocity ◽  
Longmenshan Fault Zone ◽  
Velocity Models ◽  
Longmenshan Fault

Three-dimensional P wave velocity models under the Zipingpu reservoir in Longmenshan fault zone are obtained with a resolution of 2 km in the horizontal direction and 1 km in depth. We used a total of 8589 P wave arrival times from 1014 local earthquakes recorded by both the Zipingpu reservoir network and temporary stations deployed in the area. The 3-D velocity images at shallow depth show the low-velocity regions have strong correlation with the surface trace of the Zipingpu reservoir. According to the extension of those low-velocity regions, the infiltration depth directly from the Zipingpu reservoir itself is limited to 3.5 km depth, while the infiltration depth downwards along the Beichuan-Yingxiu fault in the study area is about 5.5 km depth. Results show the low-velocity region in the east part of the study area is related to the Proterozoic sedimentary rocks. The Guanxian-Anxian fault is well delineated by obvious velocity contrast and may mark the border between the Tibetan Plateau in the west and the Sichuan basin in the east.

Observations of the Coyote Lake, California earthquake sequence of August 6, 1979

1980 ◽  
Vol 70 (2) ◽  
pp. 559-570 ◽  
Author(s):  
R. A. Uhrhammer
Keyword(s):  
San Francisco ◽  
Fault Zone ◽  
Strong Earthquake ◽  
Main Shock ◽  
B Value ◽  
Aftershock Sequence ◽  
The South ◽  
The North ◽  
Temporal And Spatial Characteristics ◽  
Largest Aftershock

abstract At 1705 UTC on August 6, 1979, a strong earthquake (ML = 5.9) occurred along the Calaveras fault zone south of Coyote Lake about 110 km southeast of San Francisco. This strong earthquake had an aftershock sequence of 31 events (2.4 ≦ ML ≦ 4.4) during August 1979. No foreshocks (ML ≧ 1.5) were observed in the 3 months prior to the main shock. The local magnitude (ML = 5.9) and the seismic moment (Mo = 6 × 1024 dyne-cm from the SH pulse) for the main shock were determined from the 100 × torsion and 3-component ultra-long period seismographs located at Berkeley. Local magnitudes are determined for the aftershocks from the maximum trace amplitudes on the Wood-Anderson torsion seismograms recorded at Berkeley (Δ ≊ 110 km). Temporal and spatial characteristics of the aftershock sequence are presented and discussed. Some key observations are: (1) the first six aftershocks (ML ≧ 2.4) proceed along the fault zone progressively to the south of the main shock; (2) all of the aftershocks (ML ≧ 2.4) to the south of the largest aftershock (ML = 4.4) have a different focal mechanism than the aftershocks to the north; (3) no aftershocks (ML ≧ 2.4) were observed significantly to the north of the main shock for the first 5 days of the sequence; and (4) the b-value (0.70 ± 0.17) for the aftershock sequence is not significantly different from the average b-value (0.88 ± 0.08) calculated for the Calaveras fault zone from 16 yr of data.

scholarly journals Evaluation of crustal inhomogeneity parameters in the southern Longmenshan fault zone and adjacent regions

2020 ◽  
Vol 24 (6) ◽  
pp. 1175-1188
Author(s):  
Xiao-Ping Fan ◽  
Yi-Cheng He ◽  
Cong-Jie Yang ◽  
Jun-Fei Wang
Keyword(s):  
Fault Zone ◽  
Lower Crust ◽  
Tectonic Deformation ◽  
Upper Crust ◽  
Crust And Upper Mantle ◽  
Study Region ◽  
Waveform Data ◽  
Longmenshan Fault Zone ◽  
Deformation Features ◽  
Longmenshan Fault

AbstractBroadband teleseismic waveform data from 13 earthquakes recorded by 70 digital seismic stations were selected to evaluate the inhomogeneity parameters of the crustal medium in the southern Longmenshan fault zone and its adjacent regions using the teleseismic fluctuation wavefield method. Results show that a strong inhomogeneity exists beneath the study region, which can be divided into three blocks according to its structure and tectonic deformation features. These are known as the Sichuan-Qinghai Block, the Sichuan-Yunnan Block, and the Mid-Sichuan Block. The velocity fluctuation ratios of the three blocks are approximately 5.1%, 3.6%, and 5.1% in the upper crust and 5.1%, 3.8%, and 4.9% in the lower crust. The inhomogeneity correlation lengths of the three blocks are about 10.1 km, 14.0 km, and 10.7 km in the upper crust and 11.8 km, 17.0 km, and 11.8 km in the lower crust. The differences in the crustal medium inhomogeneity beneath the Sichuan-Yunnan Block, the Sichuan-Qinghai Block, and the Mid-Sichuan Block may be related to intensive tectonic movement and material flow in the crust and upper mantle.

scholarly journals Temporal variations of the fractal properties of seismicity in the western part of the north Anatolian fault zone: possible artifacts due to improvements in station coverage

1995 ◽  
Vol 2 (3/4) ◽  
pp. 147-157 ◽  
Author(s):  
A. O. Öncel ◽  
Ö. Alptekin ◽  
I. Main
Keyword(s):  
Fault Zone ◽  
Statistical Significance ◽  
Rock Fracture ◽  
Aegean Sea ◽  
B Value ◽  
Temporal Variations ◽  
North Anatolian Fault ◽  
North Anatolian Fault Zone ◽  
The North ◽  
Northern Aegean Sea

Abstract. Seismically-active fault zones are complex natural systems exhibiting scale-invariant or fractal correlation between earthquakes in space and time, and a power-law scaling of fault length or earthquake source dimension consistent with the exponent b of the Gutenberg-Richter frequency-magnitude relation. The fractal dimension of seismicity is a measure of the degree of both the heterogeneity of the process (whether fixed or self-generated) and the clustering of seismic activity. Temporal variations of the b-value and the two-point fractal (correlation) dimension Dc have been related to the preparation process for natural earthquakes and rock fracture in the laboratory These statistical scaling properties of seismicity may therefore have the potential at least to be sensitive short- term predictors of major earthquakes. The North Anatolian Fault Zone (NAFZ) is a seismicallyactive dextral strike slip fault zone which forms the northern boundary of the westward moving Anatolian plate. It is splayed into three branches at about 31oE and continues westward toward the northern Aegean sea. In this study, we investigate the temporal variation of Dc and the Gutenberg-Richter b-value for seismicity in the western part of the NAFZ (including the northern Aegean sea) for earthquakes of Ms > 4.5 occurring in the period between 1900 and 1992. b ranges from 0.6-1.6 and Dc from 0.6 to 1.4. The b-value is found to be weakly negatively correlated with Dc (r=-0.56). However the (log of) event rate N is positively correlated with b, with a similar degree of statistical significance (r=0.42), and negatively correlated with Dc (r=-0.48). Since N increases dramatically with improved station coverage since 1970, the observed negative correlation between b and Dc is therefore more likely to be due to this effect than any underlying physical process in this case. We present this as an example of how man-made artefacts of recording can have similar statistical effects to underlying processes.

Distinct tectonic activities in Guangxi, China due to large earthquakes on the Longmenshan fault zone

2020 ◽  
Vol 307 ◽  
pp. 106557
Author(s):  
Huaizhong Yu ◽  
Jing Zhao ◽  
Xiaoxia Liu ◽  
Chen Yu ◽  
Chong Yue ◽  
...  
Keyword(s):  
Fault Zone ◽  
Longmenshan Fault Zone ◽  
Longmenshan Fault ◽  
Large Earthquakes ◽  
Tectonic Activities

scholarly journals Analysis of Spatiotemporal variations in mid-upper tropospheric methane during the Wenchuan Ms8.0 earthquake by three indices

2019 ◽  
Author(s):  
Jing Cui ◽  
Xuhui Shen
Keyword(s):  
Methane Concentration ◽  
Vertical Direction ◽  
Background Field ◽  
Gradient Index ◽  
Average Increase ◽  
Longmenshan Fault Zone ◽  
Deep Crust ◽  
Distribution Features ◽  
Before And After ◽  
Longmenshan Fault

Abstract. This research studied the spatiotemporal variation in methane in the mid-upper troposphere during the Wenchuan earthquake (12 May, 2008) using AIRS retrieval data and discussed the methane anomaly mechanism. Three indices were proposed and used for analysis. Our results show that the methane concentration increased significantly in 2008, with an average increase of 5.12 * 10−8, compared to the average increase of 1.18 * 10−8 in the previous five years. The Alice and Diff indices can be used to identify methane concentration anomalies. The two indices showed that the methane concentration distribution before and after the earthquake broke the distribution features of the background field. As the earthquake approached, areas of high methane concentration gradually converged towards the west side of the epicenter from both ends of the Longmenshan fault zone. Moreover, a large anomalous area was centered at the epicenter eight days before the earthquake occurred, and a trend of strengthening, weakening and strengthening appeared over time. The Gradient index showed that the vertical direction obviously increased before the main earthquake, and the value was positive. The gradient value is negative during coseismic or postseismic events. The gradient index reflects the gas emission characteristics to some extent. We also determined that the methane release was connected with the deep crust-mantle stress state, as well as microfracture generation and expansion. However, due to the lack of any technical means to accurately identify the source and content of methane in the atmosphere before the earthquake, an in-depth discussion has not been conducted, and further studies on this issue may be needed.

scholarly journals Healthcare use before and after changing disability pension policy: a regional Danish cohort study

2019 ◽  
Vol 29 (6) ◽  
pp. 1068-1073 ◽  
Author(s):  
Line J Borup ◽  
Nanna Ø Weye ◽  
Vibeke Jensen ◽  
Kirsten Fonager
Keyword(s):  
Policy Change ◽  
Disability Pension ◽  
Security Policy ◽  
Pension Policy ◽  
Healthcare Use ◽  
The North ◽  
Increased Risk ◽  
Significant Difference ◽  
Before And After ◽  
Eligibility Requirements

Abstract Background The social security policy for disability pension (DP) was changed in Denmark in 2013 and eligibility requirements were tightened. We describe and compare the use of healthcare among individuals with incident DP before and after the policy change. Methods This was a follow-up study based on data from nationwide databases. The study included individuals with incident DP aged 18–64 years and living in The North Denmark Region. We included individuals with incident DP before (2010–12, n = 6286) and after (2014–15, n = 1042) the 2013 policy change. Poisson regression was used to examine group differences in (i) contact to healthcare and (ii) hospitalization. For this purpose, we used incidence rate ratios stratified on type of contact before being awarded DP. Results We found a change of diagnoses for healthcare use towards higher proportions of cardiovascular, pulmonary, neurological and cancer diseases and lower proportion with musculoskeletal disorder in the populations being granted DP after policy changes. For individuals with psychiatric contact before being granted DP, we found no significant differences between periods in psychiatric healthcare after DP was awarded. For individuals with somatic contact before being granted DP, we found an increased risk of contact to somatic healthcare and hospitalization after DP requirements were tightened. Conclusion The study demonstrated that individuals who were granted DP after the eligibility requirements had been tightened suffered from more medical conditions and had an ongoing need for healthcare. In contrast, no significant difference in risk of psychiatric contact or hospitalization after DP was demonstrated.

Seismic Potential Around the Northeastern Edge of the Longmenshan Fault Zone as Inferred from Seismological Observations

2019 ◽  
Vol 177 (1) ◽  
pp. 37-53 ◽  
Author(s):  
Reiken Matsushita ◽  
Kazutoshi Imanishi ◽  
Makiko Ohtani ◽  
Yasuto Kuwahara ◽  
Jiuhui Chen ◽  
...  
Keyword(s):  
Fault Zone ◽  
Longmenshan Fault Zone ◽  
Seismic Potential ◽  
Longmenshan Fault

Research on Transverse Faults in the Longmenshan Fault Zone, China

2014 ◽  
Vol 1010-1012 ◽  
pp. 1380-1386
Author(s):  
Wei Feng Wang ◽  
Chuan Hua Zhu ◽  
Yan Bin Qing ◽  
Xin Jian Shan
Keyword(s):  
Remote Sensing ◽  
Fault Zone ◽  
Field Studies ◽  
Geophysical Data ◽  
Remote Sensing Images ◽  
Longmenshan Fault Zone ◽  
Geomorphic Features ◽  
Longmenshan Fault ◽  
Regional Tectonic

The Longmenshan fault zone has been a research hotspot, but fewer scholars have paid attention to its transverse faults. According to the analysis of regional tectonic, seismic activities, geomorphic features, remote sensing images, and deep geophysical data, combined with field studies, the existence, distribution and type of the transverse faults in the Longmenshan fault zone were demonstrated. Research shows that there are 9 transverse faults that lie parallel to each other approximately at ~50km intervals in the Longmenshan fault zone. And transverse faults can be divided into regional transverse faults and localized transverse faults with NW strike, nearly EW strike and nearly SN strike.

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