Sensitivity analysis of the Schlumberger monitoring array: application to changes of resistivity prior to the 1976 earthquake in Tangshan, China

摘要

Prior to the 1976 Tangshan earthquake of M 7.8, at nine out of fourteen geoelectric stations within 180 km of the epicenter, resistivity decreases were observed. During this same period, drops in water levels were recorded in seventeen deep wells in the same region. The sensitivity analysis shows that the resistivity decrease cannot be caused by a groundwater level decrease because all of the coefficients for the resistivity structure types A, H, and HA with a resistive substratum are positive. Some examples of a Schlumberger monitoring array are used to illustrate the application of the analytical approach. In order to detect resistivity changes associated with an earthquake, such an approach is useful for survey planning, checking or setting the 'search-depth' of a given array and facilitates the quantitative interpretation of resistivity data.