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The Wenchuan Ms8. 0 earthquake and the Lushan M7. 0 earthquake occurred in the north and south segments of the Longmenshan nappe tectonic belt, respectively. Based on the focal mechanism and finite fault model of the Wenchuan Ms8. 0 earthquake, we calculated the coulomb failure stress change. The inverted coulomb stress changes based on the Nishimura and Chenji models both show that the Lushan M7. 0 earthquake occurred in the increased area of coulomb failure stress induced by the Wenchuan Ms8. 0 earthquake. The coulomb failure stress increased by approximately 0. 135 – 0. 152 bar in the source of the Lushan M7. 0 earthquake, which is far more than the stress triggering threshold. Therefore, the Lushan M7. 0 earthquake was most likely triggered by the coulomb failure stress change.

Based on dislocation theory of Okada, we adopted a finite-element fault model inverted by Gavin Hayes from seismic data for the 2011 Japan Mw9.0 earthquake, and obtained the corresponding surface displacement and strain fields. The calculated displacement field is consistent with the observed GPS results in the trend of changes. Also the surface displacement and strain fields both show large variations in space.

Baseline offset in digital strong-motion acceleration record and initial velocity can produce unrealistic results for ground velocity and displacement derived from the acceleration by integration. A new method is proposed for the baseline correction and initial velocity calculation. It is based on linear least-squares fitting of the pre-event portion of velocity derived from the uncorrected acceleration data. Compared with the conventional method, which is based on removing the mean values of the pre-event portions of the acceleration and velocity traces, this method has clearer physical meaning and better stability.

To monitor changes in building tilt angles more accurately and efficiently and to safeguard the people's safety and property, a new tilt angle monitoring method was proposed in this paper. This method adopts double square artificial marks and a plumb line determined by MATLAB to record changes in the building tilt angle based on image processing technology. Two black square artificial marks with the size of 10 mm × 10 mm were placed near the side of the plumb line. A digital camera was adopted to collect tilt images which were saved in the computer. The tilt images were successively subjected to image greying, binarization, denoising, image segmentation and pixel calibration. Finally, the true length of a single pixel and tilt angle change value would be obtained. The experimental results showed that the accuracy of the method was 96% higher than the manual method. Compared with traditional manual methods and three-dimensional scanning monitoring methods, the advantages of this method are that the equipment used is relatively cheap, the image calculation workload is small and is suitable in dangerous working conditions. In conclusion, the proposed technique could accurately, concisely and effectively calculate the changes in building tilt angle and improve work efficiency. [ABSTRACT FROM AUTHOR]

We used various fault models to calculate the stress change on Ridgecrest epicentral locations and surrounding fault systems. In general, the 2019 Ridgecrest earthquake sequence was triggered by past historical earthquakes. The computed stress changes in both foreshock and mainshock epicentral locations have exceeded the stress trigger threshold, which suggests that past historical earthquakes play a key role in driving the Ridgecrest earthquake source structures closer to failure. We calculated the stress on surrounding faults imparted by the Ridgecrest mainshock and its combination with past earthquakes. The Garlock fault is generally stressed by the mainshock, with a maximum of 1.573 bar on central segment. However, our combined model yielded decreased stress on central Garlock fault. Furthermore, we calculated the expected seismicity rate on the Garlock fault and found that the central segment had a higher seismicity rate than the western and eastern segments. [ABSTRACT FROM AUTHOR]

The Mw7.5 Palu earthquake that occurred on September 28, 2018, in Indonesia caused much damage to the city of Palu. Preliminary investigations indicated that the Palu‐Koro Fault (PKF) hosted this damaging event. We calculated the seismicity before and after the 1996 Minahasa Mw7.9 earthquake and found that the seismicity on the PKF was enhanced after this earthquake. The earlier earthquake added Coulomb stress changes (∆CFS) to the seismogenic fault plane. We calculated the ∆CFS produced by the Palu earthquake on a specified received nodal plane; the results suggest that many aftershocks occurred in the region of increased ∆CFS. This region was consistent with the region of increased seismicity. The ∆CFS on neighbouring faults increased, and up to 55.282 bar of stress was observed on the PKF. Furthermore, we calculated the expected seismicity rate and found that it will require ~50 years to recover to its original level. [ABSTRACT FROM AUTHOR]