Abstract
A multi-parametric approach was applied to climatological data before the Ms 8.0 2008 Wenchuan and Ms 7.0 2013 Lushan earthquakes (EQs) in order to detect anomalous changes associated to the preparing phase of those large seismic events. A climatological analysis for seismic Precursor Identification (CAPRI) algorithm was used for the detection of anomalies in the time series of four parameters (aerosol optical depth, AOD; skin temperature, SKT; surface latent heat flux, SLHF and total column water vapour, TCWV). Our results show a chain of processes occurred within two months before the EQs: AOD anomalous response is the earliest, followed by SKT, TCWV and SLHF in the EQs. A close spatial relation between the seismogenic Longmenshan fault (LMSF) zone and the extent of the detected anomalies indicates that some changes occurred within the faults before the EQs. The similarity of time sequence of the anomalies between the four parameters may be related to the same process: we interpret the observed anomalies as the consequence of the upraising of gases from a fluid-rich middle/upper crust along pre-existing seismogenic faults, and of their release into the atmosphere. Our multi-parametric analytical approach is able to capture phenomena related to the preparation phase of strong EQs.
Highlights
Earthquake preparation is a long-term lithospheric process and it is driven by tectonic- and/or fluid-induced stress changes [1,2,3,4]
Seismological evidences of foreshocks before the Wenchuan and Lushan EQs are lacking [41,42]. This suggests that the anomalies related to the skin temperature (SKT), atmospheric optical depth (AOD), surface latent heat flux (SLHF), and total column water vapor (TCWV) are not related to stress changes induced by tectonic processes, i.e., early fracturation
On the basis of our data and the above described crustal structure of the Longmenshan fault (LMSF) system and its degassing processes, we propose that the anomalies we detect in the SKT, AOD, SLHF, and TCWV parameters before the Lushan and Wenchuan events may be due to the anomalous discharge of CH4 and CO2 along the seismogenic faults
Summary
Earthquake preparation is a long-term lithospheric process and it is driven by tectonic- and/or fluid-induced stress changes [1,2,3,4]. The changes observed during the preparation phase of large seismic events are generally explained by the lithosphere–atmosphere–ionosphere coupling (LAIC) model [7], which suggests that a diversity of phenomena might occur before EQs due to either an exchange of energy or particles between the lithosphere and the atmosphere reaching, in some cases, the ionosphere. Considering geochemical–thermal anomaly interaction of the LAIC model as a theory, the objective of this study was to observe the abnormal response of the multi-parameter data from the lithosphere and atmosphere in the seismogenic process and to further explain the EQ mechanism along the Longmenshan fault (LMSF) zone. We selected four climatological parameters: skin temperature (SKT), total column water vapor (TCWV), surface latent heat flux (SLHF) and aerosol optical depth (AOD) to represent the geochemical–thermal process of the lithosphere and atmosphere prior to EQs
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