Microwave Brightness Temperature Anomalies Associated With the 2015 Mw 7.8 Gorkha and Mw 7.3 Dolakha Earthquakes in Nepal

Abstract

Two catastrophic earthquakes (EQs) with magnitudes of Mw 7.8 and 7.3 occurred in Gorkha and Dolakha, Nepal on April 25 and May 12, 2015, respectively. By employing the spatio-temporally weighted two-step method (STW-TSM), significant positive and negative microwave brightness temperature (MBT) anomalies preceding the two EQs were uncovered with satellite microwave data from FY-3B. Two strip-shaped positive MBT anomalies appeared in the Higher Himalayan 1 day before the Gorkha shock and the Dolakha shock, respectively, which were parallel to the thrust belt and whose intensity distributions exhibited good topographic consistency with the elevation profiles of the central Himalayas. Referring to the P-hole theory and seismogenic mechanism of the Nepal EQs, seismically activated mobile positive charges are presumed to have caused the surface positive MBT anomalies by reducing the superficial dielectric constant and increasing the local temperature of the Himalayan cliffs. A significant negative MBT anomaly occurred plausibly as early as March 2015 in the southern Gangetic Plain and developed into a stripe parallel to the thrust belt on the days of the Gorkha and Dolakha events. The negative MBT anomalies are suggested to result from soil moisture increases due to local synchronous precipitation. This work presents the first case study to use data from the FY-3B microwave radiation imager (MWRI) to investigate seismic anomalies, and discriminate both positive and negative MBT anomalies preceding an EQ for the first time.