Dynamic Location Method for Shallow Ocean Bottom Nodes Using the Levenberg-Marquart Algorithm

Ocean bottom node(OBN)data acquisition is the main development direction of marine seismic exploration;it is widely promoted,especially in shallow sea environments.However,the OBN receivers may move several times because they are easily affected by tides,currents,and other factors in the shallow sea environment during long-term acquisition.If uncorrected,then the imaging quality of subsequent processing will be affected.The conventional secondary positioning does not consider the case of multiple movements of the receivers,and the accuracy of secondary positioning is insufficient.The first arrival wave of OBN seismic data in shallow ocean mainly comprises refracted waves.In this study,a nonlinear model is established in accordance with the propagation mechanism of a refracted wave and its relationship with the time interval curve to realize the accurate location of multiple receiver movements.In addition,the Levenberg-Marquart algorithm is used to reduce the influence of the first arrival pickup error and to automatically detect the receiver movements,identifying the accurate dynamic relocation of the receivers.The simulation and field data show that the proposed method can realize the dynamic location of multiple receiver movements,thereby improving the accuracy of seismic imaging and achieving high practical value.

Tectonic setting of the seismogeny of the 1976 Tangshan,ChinaM=7.8earthquake

Based on the analysis of multi-temporal and multi-spectral satellite images for North China region, we have found that one year and more before the occurrence of 1976 Tangshan earthquake, the anomalies of electro-magnetic radiation on the satellite images indicated that the NE-trending Tangshan fault zone was dissected by the NNW-trending Nantai-Tangshan fault, and the Changping-Fengnan fault was dragged to form an arcuate bending at Fengnan. All these indicate the right-lateral translation along the Tangshan fault in NE direction. In order to gain an insight into the features of these faults, a shallow seismic exploration along the Tangshan and Changping-Fengnan faults has been carried out. The results have indicated that the NE-trending Tangshan fault is a high angle right-lateral strike-slip normal fault, dipping northwest, while the NWW-trending Changping-Fengnan fault is a southwest-dipping left-lateral strike-slip normal fault.

Tectonic activity and earthquake risk in the Chengnanhe fault zone in Weihai city,Shandong province,China,obtained by using an integrated prospecting technique in geophysics and geology

For city planning and reducing potential earthquake risk,it’s necessary to detect the information of the buried faults in an urban area especially,including the location and activities.An integrated technique with geophysical and geological methods,including the shallow seismic reflection profile,electrical resistivity measurement,geologic borehole section,and exploration trench,was used to detect the Chengnanhe fault,which is one of the two main faults passing through the Weihai urban area in Shandong province,China.The results show that it is a normal fault striking with E-W direction,and it is relatively inactive and stable.By using the thermoluminescence(TL)dating,we found that the Chengnanhe fault initiated in mid-Pleistocene and there was no offset after late Pleistocene.Such an integrated technique with multiple geological and geophysical methods provides a significant assessment of earthquake risk for city planning in urban areas.