The Sensitivity of the Loa/Unload Response Ratio and Critical Region Selection Before Large Earthquakes

Abstract

Occurrence of a large earthquake could be predicted by anomalous temporal increase of the Load/Unload Response Ratio (LURR). Previous studies have indicated that the stress field that existed before a large earthquake may have a strong influence on the evaluation of LURR. In this paper, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. This algorithm is devised to increase the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. In the algorithm, we assess the stress change and identify the areas with increased Coulomb stress before an earthquake using a simple back-slip dislocation model of the event. Retrospective tests of this algorithm on some disastrous earthquakes that occurred in the Chinese mainland in recent years show remarkable enhancement of the LURR precursory anomalies. By using the hypothetical faults for the large earthquake prediction, we further illustrate that the new algorithm is more sensitive to detect future earthquake of a particular magnitude range and location than the circular region algorithm. Hence, where sufficient information of the regional fault tectonics is given, the Coulomb stress algorithm can be used to augment current LURR technique for seismic hazard estimation.