The 2009 L’Aquila MW 6.3 earthquake: a new technique to locate the hypocentre in the joint inversion of earthquake rupture process

A new technique is presented to jointly invert the teleseismic and Interferometric Synthetic Aperture Radar (InSAR) data by simultaneously searching for the hypocentre and the relative weight of InSAR data. In this technique, the parameters of causative fault is determined by using InSAR data first, and then the hypocentre is searched for by jointly inverting teleseismic and InSAR data with the assumption that each subfault on the fault is a potential hypocentre. With this technique, we investigated the source rupture process of the 2009 April 6 L’Aquila MW 6.3 earthquake without the use of the existing hypocentre locations. Our estimated hypocentre is 42.366°N, 13.385°E, depth 6.9 km, with an uncertainty of 1∼2 km, similar to the hypocentre (42.348°N, 13.380°E, depth 9.5 km) determined by National Institute of Geophysics and Volcanology (INGV) using arrival time data within the epicentral distance of 50 km. Our joint inversion suggests a scalar moment of 3.5 × 1018 Nm, equivalent to a moment magnitude of MW 6.3. The source process consists of two subevents with a total duration of 7.7 s. The first event (0∼3 s) corresponds to the slip patch near the hypocentre and the second (in the next 4.7 s) ruptured the other slip patch at 4∼16 km along the strike direction. These unilateral rupture characteristics of the L’Aquila earthquake are confirmed by the apparent source time functions (ASTFs) analysis. In addition, two resolution tests are performed to check the reliability of this work, clarifying the differences between the inversion results with teleseismic data only, InSAR data only and joint inversion, indicating that a higher resolution can be achieved through the joint inversion