Automatic generation of seismic source models using Sentinel-1 DInSAR coseismic maps obtained through the EPOSAR service

In this work we present a processing chain we implemented to calculate, in a completely automatic way, the seismic source with distributed slip starting from the Differential Synthetic Aperture Radar Interferometry (DInSAR) coseismic displacement maps generated through the EPOSAR service.

EPOSAR is a scientific service of EPOS (European Plate Observing System) Research Infrastructure, developed by CNR-IREA, that provides coseismic displacement maps at global scale. In particular, following the occurrence of an earthquake of a) magnitude greater and b) depth smaller than selected thresholds, EPOSAR automatically retrieves and process all the Copernicus Sentinel-1 data necessary to generate all the possible DInSAR coseismic maps within a monthly time window, so that the earthquake can be analyzed from different satellite paths. We further remark that the EPOSAR service is currently operative and the generated DInSAR products are freely available to the scientific community through the EPOS infrastructure.

In this work we present the implementation of an automatic new modeling chain, by acting in cascade to the EPOSAR service, with a twofold aim: revealing the seismic source at the occurrence of every new event detectable through DInSAR and providing a complete database of sources that includes all the earthquakes occurred since the launch of Sentinel-1 satellites.

The procedure starts from DInSAR data, produced by the EPOSAR service, and a focal mechanism automatically retrieved from several catalogs (USGS, Global CMT, INGV-TDMT). The non-linear inversion is implemented with two stages, coarse and refined, to get a robust and well centered, uniform slip solution; this source is then extended and subdivided into small elements to get the slip distribution via linear inversion. For every single step, a number of algorithms, based on two decades of experience in modeling at INGV, were implemented to face the large number of options and conditions usually handled by an expert user: image selection, setup and iterative update of the input parameters, definition of the regularization strength,  detection of specific conditions (point-source, poorly constraining data, etc.). The model is also automatically updated with the availability of new DInSAR data, always balancing the contribution from ascending and descending acquisitions.

The developed tool is designed to deploy a service aimed at providing a quick and reliable automatic fault model solution and it has been tested and validated on hundred up to date events, characterized by different magnitudes, rupture mechanisms and locations. In this work, we present the main algorithm aspects and performances, addressing also the potentialities arising with the availability of a complete and homogeneous database of DInSAR-based source models: definition of updated scaling factors, systematic bias, etc.

We finally remark that our tool will be soon operative and integrated within the EPOS infrastructure, thus allowing the user community to access the generated results and benefit from quick and reliable products on the source mechanisms of the more significant seismic events.