No abstract

We conduct a systematic survey of remote triggering of earthquakes in north China following the 2008 M w 7.9 Wenchuan earthquake. We identify triggered earthquakes as impulsive seismic energies with clear P and S arrivals on 5 Hz high-pass-filtered three-component velocity seismograms during and immediately after the passage of teleseismic waves. We find clearly triggered seismic activity near the Babaoshan and HuangzhuangGaoliying faults southwest of Beijing, and near the aftershock zone of the 1976 M w 7.6 Tangshan earthquake. While several earthquakes occur during and immediately after the teleseismic waves in the aftershock zone of the 1975 M w 7.0 Haicheng earthquake, the change of seismicity is not significant enough to establish the direct triggering relationship. Our results suggest that intraplate regions with active faults associated with major earthquakes during historic or recent times are susceptible to remote triggering. We note that this does not always guarantee the triggering to occur, indicating that other conditions are needed. Since none of these regions is associated with any active geothermal or volcanic activity, we infer that dynamic triggering could be ubiquitous and occur in a wide range of tectonic environments.

No abstract

When noise in the field is very strong, we can not get data with proper signal to noise ratio (SNR) even if combination vibroseis is used. To solve this problem we proposed to apply a phased‐array vibrator, which can form a directional seismic wave. We have made numerical simulation of multi‐track seismograms and computed reflected waves’ SNR for combination and phased‐array sources on a given horizontal stratified model. The result shows that the average SNR of reflected waves increases by 1.54_9.90dB with respect to the combination source when 4,8,15 and 20‐unit phased‐array vibrators are used. We conclude that phased‐array source is competent to improve seismic signal SNR. Moreover, the phased‐array source can boost SNR obviously when more vibrators are applied but there is no similar result for the combination source.