Abstract
Constraining the point source parameters of the 11 November 2019 Mw 4.9 Le Teil earthquake using multiple relocation approaches, first motion and full waveform inversions
Highlights
The dip of the SE-dipping nodal plane corresponding to the fault is not well constrained by waveform inversion, but the focal mechanism at rupture initiation determined with the first motions suggests that fault dip may be constant (50°–60°) from the surface down to 1–1.5 km depth
Focal mechanisms determined by waveform inversion for the Le Teil mainshock in the days following its occurrence, as summarized on the EuropeanMediterranean Seismological Centre (EMSC) web page concur in the dominant reverse faulting component, with NE–SW nodal planes
Using ten post-seismic stations well-distributed around the rupture zone and with epicentral distances smaller than 5 km, we obtained a reference average location for the aftershock: 44.5198 N, 4.6713 E, and 1.8 km depth
Summary
With a local magnitude (ML) of 5.4 (CEA-DASE, Commissariat à l’Energie Atomique et aux Energies Alternatives—Département analyse, surveillance, environnement) and a moment magnitude (Mw) of 4.9 [Cornou et al, 2021, Ritz et al, 2020], the 11 November 2019 Le Teil earthquake (10h52 UTC) is one of the strongest and most destructive earthquakes that occurred in the last decades in metropolitan France. We called the method GRIDSIMODLOC as it combines a grid search, a simulated annealing, and an optimization of the 1D velocity model In recent years, this method, combined with the FMNEAR waveform inversion used in the present study [Delouis, 2014], has been applied to several earthquakes of moment magnitude Mw 3.2 to 4.9 in France and results have been published on the BCSF special events web pages [e.g., BCSF, 2018, 2019a,b, 2020]. Focal mechanisms determined by waveform inversion for the Le Teil mainshock in the days following its occurrence, as summarized on the EuropeanMediterranean Seismological Centre (EMSC) web page (https://www.emsc-csem.org/Earthquake/ earthquake.php?id=804595#map) concur in the dominant reverse faulting component, with NE–SW nodal planes They display large variations in the dip angles (37° to 57°) and in the depth (1 to 13 km). The analysis is complemented by the determination of the focal mechanism of the mainshock and its aftershock with the available first motion data
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