Pre-earthquake MBT anomalies in the Central and Eastern Qinghai-Tibet Plateau and their association to earthquakes

Abstract

Thermal anomalies prior to large and hazardous earthquakes have been extensively detected by thermal infrared and microwave remote sensing techniques. However, few of the current research focuses on long-term tracking of the thermal anomalies for decades and their earthquake prediction potential in a seismically active area. Targeting at exploiting the association of thermal anomalies to earthquakes in terms of time, spatial patterns and magnitudes, comprehensive statistical analysis on the pre-earthquake microwave brightness temperature (MBT) anomalies of 103 destructive earthquakes with Ms. ≥ 5.0 in the Central and Eastern Qinghai-Tibet Plateau (90° E – 102° E, 28° N – 38° N) is conducted. To detect robust pre-earthquake thermal anomalies buried by the complex background and frequently variant meteorological noise, we propose a wavelet-based two-step difference (WTSD) approach which incorporates hierarchical clustering and wavelet decomposition, adopting it on the 17 years' microwave data collected by AMSR-E and AMSR-2 sensors. Interestingly, an NE trending MBT increase stripe has been repeatedly occurring prior to 60 of the 103 earthquakes (accounting for 58.25%). Then, we conduct comprehensive statistics on the occurring time, spatial patterns and intensities of the MBT anomalies, and find them closely associated to seismic events with Ms. ≥ 5.0 occurred in the Bayan Har and Qiangtang blocks. And, the MBT anomaly stripe is spatially consistent with the NE trending extensional faults and geothermal fields in this study area. Furthermore, the possible source mechanism of the MBT anomalies is explored with rock loading microwave observation experiments, and possible physical models suggested by predecessors are also discussed. On this basis, we discuss the relationship between the pre-earthquake MBT anomalies and extensional faults, and speculate the MBT anomalies are probably caused by intensified extrusion of the Indian plate to the Eurasian plate and the increased crustal stress, which indicates their significant potential as earthquake precursors in the Central and Eastern Qinghai-Tibet Plateau.