The largest induced earthquakes during the GEOVEN deep geothermal project, Strasbourg, 2018–2022: from source parameters to intensity maps

Abstract

SUMMARYBetween 2019 November and 2021 July, four induced earthquakes of local magnitude equal to or greater than than three were felt by the population of Strasbourg, France. These events were related to activity at the deep geothermal site GEOVEN located in Vendenheim in the northern suburb area of the city of Strasbourg. The first earthquake, with a local magnitude (Mlv) of 3.0, occurred on 2019 November 12, at the same depth as the bottom of the wells (approximately 4 km) but 5 km to the south. The second (Mlv 3.6) occurred a year later, on 2020 December 4, below the wells, and led to the termination of the project by the authorities. The third (Mlv 3.3) was initiated three weeks after shut-in on 2021 January 22, while the largest earthquake to date (Mlv 3.9) occurred on 2021 June 26, more than 6 months after shut-in. We constrained these four events’ absolute locations using a 3-D velocity model of the area and here present regional intensity maps. We estimated moment magnitude and focal mechanism trough waveform inversion and inferred the fault plane activated during the largest event from an analysis of rupture directivity effects in the recorded waveforms. Our analysis highlights the existence of a critically stressed fault that hosted three of these widely felt events. We show how the derived source properties of these four earthquakes are directly linked to ground shaking observations at the surface. Notably, we demonstrate how earthquake moment, location, direction of rupture and stress drop impact the regional intensity distribution. Our results suggest that the traffic light system could benefit from including ground shaking scenarios based on realistic subsurface properties and potential earthquake source models.