Multi-fault rupturing of the 2019 Mw4.6 Rongxian shallow earthquake in the Sichuan Basin, China and its implication for hazard analysis

• Both geodetic and seismic data reveal the 2019 Rongxian earthquake ruptured two shallow, distinct faults. • Two foreshocks and the mainshock's first subevent facilitated the second subevent through pore pressure increase and fault reactivation due to hydraulic fracturing. • Multi-fault interactions pose challenges in seismic risk assessment for shallow industrial fluid injections. Multi-fault rupturing phenomena are crucial for understanding earthquake source processes and assessing their potential maximum magnitudes. Currently, the multi-fault phenomena have frequently been found for large tectonic earthquakes. For fractures at much smaller scales, multiple-crack events have also been observed in laboratory rock experiments. However, the phenomena are less reported for small-to-moderate earthquakes. In this study, we use both geodetic and seismic data to determine reliable rupture processes of the 2019 Mw 4.6 Rongxian earthquake in a shale gas field in the Sichuan Basin, China. Our results reveal that the Mw 4.6 mainshock ruptured two shallow, sub-parallel faults. This finding provides a bridge for understanding the complex source processes between tiny laboratory earthquakes and large tectonic earthquakes, and pose challenges to seismic risk and hazard assessment in areas associated with industrial productions.