A speleoseismological study has been conducted at over a dozen cave sites along the Longmen Shan fault zone of the eastern Qinghai-Tibet Plateau. The aim was to assess the damage inflicted on ...speleothems by the Mw 7.9 Wenchuan earthquake. Results show that the earthquake led to either partial or complete collapse of the caves. ‘Soda straws’ are shown to be particularly vulnerable to earthquake damage, but statistical analyses indicate that the spindle and slender shapes are also very likely to break. Cave depth is also shown to play an important role in the fracture development during the earthquake. The measured orientations of fallen stalactites are preferentially aligned to the coseismic surface offset peaks and therefore to the direction of earthquake wave propagation. Several such damaged speleothems resulting from sudden co-seismic movements were observed. The direction of ceiling (hanging wall) movement caused by the Wenchuan earthquake is NW-NNW, consistent with block motion on the footwall of the Yingxiu-Beichuan fault. We inferred that the faults in the caves were not co-seismic structures of the Wenchuan earthquake; but instead they are likely normal faults as the result of gravity creeping induced by the earthquake.
•Speleothem damage related to the 2008 Wenchuan (China) earthquake are documented.•Damage evidence recorded by field measurement with guidance from local population.•Damage includes cave collapse, involving broken stalactites and fracture development.•Damage extent and type linked to cave depth and seismic wave propagation.•Cave faulting indirectly linked to co-seismic reactivation and gravity collapse.
The 7th IEEE/ACIS Conference and the 2nd IEEE/ACIS Workshop on e-Activity (IWEA 2008) featured researchers from around the world. The conference organizers selected 23 outstanding papers for this ...volume of Springer's Studies in Computational Intelligence.
Abstract
Global Positioning System (GPS) stations installed in and around the epicenter of the Lushan earthquake (Mw 6.7), which occurred almost 5 years after the 2008 Wenchuan earthquake, recorded ...preseismic deformation corresponding to the Lushan earthquake within the southern Longmenshan thrust belt. A half-space dislocation model is used to simulate the theoretical values of the postseismic displacements caused by the 2008 Wenchuan earthquake, and after transforming the reference frame and filtering the GPS displacement time series, the theoretical and observed GPS values are compared to identify the geodetic anomaly preceding the Lushan earthquake. The abnormal extent of this geodetic anomaly decreases with increasing epicentral distance for each GPS site. This geodetic signal reflects preslip along a locked section of the 2013 seismogenic fault, which caused the accumulation of elastic strain energy until the faulting strength was overcome, thereby generating the Lushan earthquake. Hence, this anomaly might be used as an observable and identifiable precursor to forecast an impending earthquake within a period of less than two and half years before its occurrence.
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•Different seismic phenomena occurred in a small and large sedimentary basins.•Seismic effects of the basin edge and soil layers of the small sedimentary basin.•Simulating of ...high-frequency (up to 10 Hz) seismic wave propagation.
In this study, the ground motions that can be attributed to the aftershocks of the 2008 Mw7.9 Wenchuan, China earthquake recorded in the Wudu basin, which is a small basin in the eastern Tibetan Plateau, are analyzed to investigate the seismic effect of a small sedimentary basin. In case of the Wudu basin, the site responses from the basin edge are stronger than those from the basin center; the monitoring sites located near the Wudu basin edge and the Wudu basin center are sensitive to the low-frequency (<3 Hz) and high-frequency (>5 Hz) components of ground motion, respectively. It indicates that some different seismic phenomena occurred in a small sedimentary basin compared with a large sedimentary basin. To further study the ground motion in a small sedimentary basin, a simulation of the Wudu basin was conducted using the finite element method with a viscous–elastic artificial boundary. The grid size of the surface layer of the basin is 2.5 × 2.5 m2, and high-frequency (up to 10 Hz) components of a synthetic waveform were obtained. The simulation denoted that the surface wave initially appeared in the Wudu basin edge and subsequently propagated into its interior. The near-surface soil layers, exhibiting a relatively low wave velocity, magnified the amplitude of the seismic wave in the Wudu basin. Furthermore, the numerical simulation results are basically consistent with the actual ground motion records, especially with the same predominant frequencies of ground motions at the sites located near the Wudu basin edge.
In this study, we propose an empirical method for the probabilistic prediction of travel distance from landslide areas in an earthquake-induced landslide and then verify the applicability of the ...proposed method. In order to propose a probabilistic prediction method, we analyze the relationship between the travel distance (L) and landslide areas (A) in cases of landslides triggered by the Niigata-Chuetsu earthquake, the Iwate-Miyagi Nairiku earthquake, and the 2016 Kumamoto earthquake. We found that there was a power-law relationship between the measured travel distance and landslide area. This suggests that the travel distance might be predicted using the landslide area. However, the travel distances were largely scattered. Therefore, we propose a formula that can predict the probability of travel distance using F(r), which is the cumulative distribution function of the normal distribution of the ratio of the predicted and measured travel distance, Ri, since we find that it shows normal distribution in our three cases. In order to verify the proposed formula, we prepared training and test datasets for each case of the three earthquakes. Further we verified how much the probability of the travel distance in test datasets could be described by the proposed method.
SUMMARY
We present a source inversion of the 2008 Wenchuan, China earthquake, using strong-motion waveforms and geodetic offsets together with 3-D synthetic ground motions. We applied the linear ...multiple time window technique considering geodetic and dynamic Green's functions computed with the finite-element method and the reciprocity and Strain Green's Tensor formalism. All ground motion estimates, valid up to 1 Hz, accounted for 3-D effects, including the topography and the geometry of the Beichuan and Pengguan faults. Our joint inversion has a higher moment (M0) than a purely geodetic inversion and the slip distribution presents differences when compared to 1-D model source inversions. The moment is estimated to be M0 = 1.2 × 1021 N·m, slightly larger than other works. Our results show that considering a complex 3-D structure reduces the size of large areas of 10 m slip or greater by distributing it in wider zones, with reduced slips, in the central portion of the Beichuan and the Pengguan faults. Finally, we compare our source with a relocated aftershock catalogue and conclude that the 4–5 m slip contours approximately bound the absence or presence of aftershocks.
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7.9 Wenchuan earthquake in China caused widespread soil liquefaction and ground failures. A liquefaction case study of gently sloping ground at Yingxiu Town in the near-fault region is ...presented, which features its relatively thick deposits of sand-gravel mixtures, high soil stiffness, extremely intensive ground motion, large lateral spreading and severe damage of superstructure. The details of ground motion, site condition, field manifestations of liquefaction, subsurface soil profiles and field testing of shear wave velocities are presented. A conceptual binary mixture model is proposed to explain the gravel content effect on the stiffness and liquefaction resistance of gravelly soils. A preliminary liquefaction triggering evaluation method for gravelly soils is proposed by considering the gravel content correction of shear wave velocities based on the existing simplified procedure for typical sandy soils. The failure mechanism of the Baihua Bridge built at this site is explored, and the liquefaction-induced lateral spreading in down-slope direction might aggravate the failure process by imposing a large kinematic load on the piers besides the inertial forces transferred from the superstructure.
This article presents the difference in patterns of NGOs’ post-disaster reconstruction between the 2008 Wenchuan earthquake and the 2013 Lushan earthquake based on a case study of the One Foundation. ...The comparative studies of the One Foundation’s activities during the two responses illustrate that the organizational strategy gradually shifted from “resource-based” to “learning-based”. Their approach evolved from the providing of resources to the providing of knowledge, as they transformed both aid providers and recipients into collaborative learners, changed a resource-delivery organization into a learning organization and shaped a decentralized partnership of organizations into a mutual learning ecosystem in which knowledge flowed in multiple directions. This example of the One Foundation illustrates the potential future directions of NGOs' participation in disaster response in China.
Global navigation satellite system (GNSS) displacements at near‐source stations can be biased in both amplitude and phase due to fierce earthquake strike. We propose to inject inertial measurement ...unit (IMU)‐recorded ground motions into GNSS receivers to compensate their phase‐lock loops (PLLs) for seismic motion stress, aiming at keeping steady carrier‐phase tracking. We use a shake table to replay an acceleration record (0.5–2.0 g) from the 2008 Mw7.9 Wenchuan earthquake to test this IMU‐augmented PLL: It achieves a 1.9‐mm amplitude error (RMS) and an 8.0‐ms phase lag against the shake table's recordings, while the conventional PLL languishes to 6.0 mm and 56.5 ms, respectively. Moreover, the IMU‐augmented PLL enables a six‐degree‐of‐freedom integration among the GNSS and IMU data, where the displacement amplitude error and phase lag decline further to 0.9 mm and 3.5 ms, respectively. We believe that the IMU‐augmented GNSS receivers are ideal strong‐motion seismograph to capture trustworthy broadband displacements in the near fields.
Plain Language Summary
Understanding the origin and mechanism of destructive earthquakes is predicated on the faithful recordings of their induced ground displacements near the significantly deformed epicentral regions. Global navigation satellite system (GNSS) receivers have been recognized as the best tool to measure the large epicentral displacements. This is achieved within the GNSS receivers by continuously tracking the satellite carrier‐phase signals. However, GNSS receivers are likely to lose their fidelity in recording complete and accurate displacement waveforms in case of strong ground motions, since their carrier‐phase tracking becomes unstable when strained by such persistent and high dynamic stress. We hence developed an advanced GNSS receiver architecture where the dynamic stress suffered by the carrier‐phase tracking components is compensated for by an embedded inertial measurement unit consisting of one accelerometer and one gyroscope. In this case, the carrier‐phase signals can be tracked steadily by GNSS receivers, and the displacement accuracy can be improved from subcentimeter to millimeter level by about 70% when the ground accelerations reach up to twice the gravitational acceleration. We believe that this advanced GNSS receiver will be an excellent strong‐motion seismometer in recording displacements directly at a few millimeter resolution without missing or distorting any earthquake signals, even in case of fierce ground motions.
Key Points
A new GNSS receiver architecture is developed by embedding both accelerometer and gyroscope to capture fierce seismic displacements
GNSS displacement error and phase lag are both reduced by 70% and 85% to 2 mm and 8.0 ms, respectively, compared to conventional receivers
Six‐degree‐of‐freedom seismogeodesy is achieved with the displacement error and phase lag reduced further to 0.9 mm and 3.5 ms, respectively
In 2008, the Mw 7.9 Wenchuan earthquake killed >80,000 and injured more than 370,000 people in the province of Sichuan, China. About 5 years later, Mw 6.6 Lushan earthquake occurred on 20 April 2013, ...only ~90 km further south. More recently, in 2017, a third event, Mw 6.5 Jiuzhaigou earthquake, occurred ~250 km north of the Wenchuan earthquake epicenter. These events were all along the Longmen Shan thrust belt in eastern Tibet. The questions posed by these events still reverberate in the Chinese and international geoscience communities. In this special section, we summarize and report new data sets, observations, and modeling results of the eastern Tibet during the last decade. It covers the tectonics of eastern Tibet, the seismology, and the surface response of the earthquake. All these contributions will provide new insights into the geodynamics of the eastern Tibet. We further highlight a number of outstanding questions that remain to be addressed.
Key Points
We summarize and report new data sets, observations, and modeling results of the eastern Tibet during the last decade.
All these contributions will provide new insights into the geodynamics of the eastern Tibet.
We further highlight a number of outstanding questions that remain to be addressed.
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