Multi-Parametric Climatological Analysis Reveals the Involvement of Fluids in the Preparation Phase of the 2008 Ms 8.0 Wenchuan and 2013 Ms 7.0 Lushan Earthquakes

Abstract:

Atmospheric aerosol refers to a multiphase system composed of various solid and liquid particles as well as gas carriers suspended in the atmosphere, with particle diameters mostly distributed between 0.01 and 100 µm. Natural dust, oceanic particles and human activities are all sources of aerosol particles. Aerosol optical depth (AOD) is the most basic optical characteristic of atmospheric aerosol and is an important index used to characterize atmospheric turbidity. 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.