Geosphere coupling and hydrothermal anomalies before the 2009 M_w 6.3 L'Aquila earthquake in Italy

Abstract. The earthquake anomalies associated with the 6 April 2009 M_w 6.3 L'Aquila earthquake have been widely reported. Nevertheless, the reported anomalies have not been so far synergically analyzed to interpret or prove the potential lithosphere–coversphere–atmosphere coupling (LCAC) process. Previous studies on b value (a seismicity parameter from Gutenberg–Richter law) are also insufficient. In this work, the spatiotemporal evolution of several hydrothermal parameters related to the coversphere and atmosphere, including soil moisture, soil temperature, near-surface air temperature, and precipitable water, was comprehensively investigated. Air temperature and atmospheric aerosol were also statistically analyzed in time series with ground observations. An abnormal enhancement of aerosol occurred on 30 March 2009 and thus proved quasi-synchronous anomalies among the hydrothermal parameters from 29 to 31 March in particular places geo-related to tectonic thrusts and local topography. The three-dimensional (3-D) visualization analysis of b value revealed that regional stress accumulated to a high level, particularly in the L'Aquila basin and around regional large thrusts. Finally, the coupling effects of geospheres were discussed, and a conceptual LCAC mode was proposed to interpret the possible mechanisms of the multiple quasi-synchronous anomalies preceding the L'Aquila earthquake. Results indicate that CO₂-rich fluids in deep crust might have played a significant role in the local LCAC process.