Referring to the first law of geography and its extension in time domain, this research makes improvements on the two-step method (TSM) presented to retrieve seismic microwave brightness temperature (MBT) anomaly, and a new method named spatio-temporally weighted TSM (STW-TSM) is developed. Temporally weighted background is calculated using nonseismic data according to respective time intervals with the shocking year, and applied to remove long-term trend so as to retrieve basic MBT residuals. Spatially weighted background is calculated referring to Euclidean geospatial distance away from the epicenter, and applied to eliminate local meteorological noise so as to retrieve cleaned MBT residuals. With May 2008 Wenchuan earthquake sequence being a case study, significant seismic MBT anomalies at H and V polarizations, 10 days before and after the May 12 Mw7.9 main shock, were retrieved using STW-TSM at 6.9, 10.7, 18.7, and 36.5 GHz, respectively. This study shows that the newly developed STW-TSM is much more qualified. More significant seismic MBT anomalies at H polarization was retrieved as compared to V polarization. More detailed and localized MBT anomalies was uncovered from high frequency bands at 18.7 and 36.5 GHz, while much remarkable anomalies (but less details) were obtained from low frequency bands at 6.9 and 10.7 GHz. This research is valuable for satellite MBT observation, seismic anomaly analysis, and earthquake precursor study. Index Terms-Advanced Microwave Scanning Radiometer for the Earth Observing System, microwave brightness temperature (MBT), seismic anomaly, spatio-temporally weighted, two-step method (TSM). I. INTRODUCTION E ARTHQUAKE is one of the major natural disasters, whose the monitoring as well as forecasting is of great challenge. However, the satellite remote sensing is providing unprecedented opportunity to monitor seismic activity of planet Earth,
Significant anomalous hydrogeochemical changes in hot spring water are detected during strong seismic cycles. It is now necessary to clarify the relationship between tectonic movements, earthquakes and the evolution of hot springs. In this paper, laboratory analyses of major, trace elements, δD, δ18O and 87Sr/86Sr values of 28 hot spring waters in the Jinshajiang fault zone (JSJFZ) in the northwestern boundary of the Sichuan-Yunnan block were conducted. The results showed that the primary source of water for JSJFZ hot springs was atmospheric precipitation. The geothermal reservoir temperature variation based on the silicon enthalpy mixing model ranged from 73 to 272°C. And the circulation depth range was 1.2–5.4 km. The segmentation characteristics of the 87Sr/86Sr values were related to the influence of source rocks on groundwater cycle processes. A conceptual model of the hydrologic cycle of hot springs explained the spatial distribution of earthquakes associated with tectonic movements. The Batang segment had the strongest water-rock reaction, the highest reservoir temperature and the deepest circulation depth; meanwhile, it was also an earthquake prone area. The fluid circulation of the JSJFZ corresponds well with the seismicity, which indicates that the hydrological characteristics of the hot spring water in a fracture zone play a crucial role in receiving information on seismic activity.
Geochemical investigation on the origin and circulation of geothermal water is crucial for better understanding the interaction between hydrosphere and lithosphere. Previous studies on the Himalayan geothermal belt mainly distributed in the central and eastern Tibetan Plateau. In this study, water samples (8 hot springs and 1 cold spring) from the Karakorum fault (KKF) zone of western Tibetan Plateau were analyzed for the hydrogeochemical characteristics and isotopic compositions. Three types of spring water along the KKF were classified on basis of ionic concentration and Sr isotopic composition: type A water (HCO3–Mg or Ca), type B water (HCO3–Na) and type C water (Cl–Na). Type A water is originated from the infiltration of meteoric water and the dissolution of silicate/evaporite. Type B water is mainly leached from the metamorphic and granitoid rocks. Type C water is formed by the dissolution of chlorides and sulphates. δD and δ18O isotopes indicate that geothermal fluid along the fault zone was mainly recharged by local precipitation. Moreover, reservoir temperatures of 144.2–208.6°C were estimated by the silica–enthalpy mixing model, and the thermal waters have a relatively deep circulation depth (≥ 7.0 km). Meanwhile, the thermal waters are characterized by extremely high Li, B, Fe and As concentrations and earthquakes frequently happened in the vicinity, suggesting that the KKF is a deep and active fault, which also indicates that the thermal fluids are strongly associated with seismicity. Therefore, thermal fluid can potentially be used as continuous monitoring sites for earthquake forecasting.
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