Locating micro‐seismic epicenters in common arrival time domain

Abstract

Accurate location of micro‐earthquake epicenters is a key component in the analysis of passive seismic data. We present a new imaging condition for migration of passive seismic data that has the advantage of minimizing unfocused noise, commonly encountered when conventional migration imaging condition is employed. This improvement is achieved by changing the definition of time at which migrated cubes are constructed. When conventional imaging condition is applied, 3D cubes are formed by collapsing seismic energy emitted from sources with a Common Initial Time (CIT). Under the new imaging condition, a migrated cube at certain time is constructed by focusing seismic energy that arrives at the receiver array the same time, i.e., principle of Common Arrival Time (CAT). It will be shown that the CAT imaging condition is more resistant to coherent noise than the CIT condition. Therefore, the new imaging condition can simplify the automatic detection of micro‐earthquake epicenters derived from the migrated cubes. The applicability and benefits of the proposed imaging condition will be shown with a series of examples using both synthetic and field passive seismic data.