Bayesian inversion of seismic spectral ratio for source scaling: Application to a persistent multiplet in the western Corinth rift

Abstract

We propose a method to precisely estimate earthquake source parameters as magnitude, size of rupture, stress drop, and coseismic slip, and their uncertainties. This method, which relies on a Bayesian approach, allows the determination of the scalar seismic moment, corner frequency (fc), and their associated uncertainties, by inverting ratios between seismic displacement spectra of nearby located earthquakes. We apply this method to a large earthquake multiplet (56 events) located under the northern coast of the Corinth gulf at 8 km depth. This multiplet is regularly active between 2001 and 2007. Results show fcP/fcS ratios globally between 1.0 and 1.5 which is compatible with the values predicted by Madariaga's circular rupture model. In detail, six earthquakes, however, exhibit corner frequency variations as a function of the station azimuth compatible with linear rupture propagation. Magnitude ranges 1.08 and 2.80 with a b value of 1.04. Source rupture length globally ranges between 40 and 170 m for stress drop between 1 and 100 MPa. We show that the number of ruptures and the cumulated coseismic slip are maximal at the center of the multiplet: this suggests that Multiplet‐866 could be seen as a weak seismogenic patch surrounded by a locked fault. However, the large value of the maximum coseismic slip cumulated over the period 2000–2008 (10 cm) rather suggests creep allowing rapid stress reloading and repeated earthquakes with short delays. We therefore propose that Multiplet‐866 is surrounded by a heterogeneous fault surface with both locked and creeping areas.

Stress‐Drop Variability of Shallow Earthquakes Extracted from a Global Database of Source Time Functions

“…also have to convert the values of T obtained from the SCAR-DEC database into f c values. This T -f c relationship is dependent on the source model (see the appendix of Godano et al, 2015). In some classes of STF models (Brune's STF, isosceles triangle), the relation between f c and the inverse of the half-pulse duration is very close to 0.3 (Madariaga, 1976;Kaneko and Shearer, 2015;Madariaga, personal comm.).…”

Inferring fault mechanical conditions from the source parameters of a complex microseismic multiplet in the Corinth rift, Greece

“…Moreover, these clusters of small earthquakes sometimes involve more than one asperity. Such complex clusters have, for instance, been reported in the Parkfield area [ Lengliné and Marsan , ; Dublanchet et al , ] and constitute the main feature of the seismic activity recorded in the Gulf of Corinth [ Lambotte et al , ; Godano et al , , ].…”

“…Before and after this period, data are either not available or not yet analyzed. Figure indicates the main characteristics of multiplet 866 proposed by Godano et al []. The characteristics can be summarized as follows: (1) a succession of 56 events with magnitudes ranging between 1.1 and 2.9 ruptured patches (asperities) within a 1 km long planar structure dipping approximately at 30° to the north and situated on the western edge of the inferred rupture plane of the 1995 M w 6.2 Aigion earthquake [ Bernard et al , ; Godano et al , ], (2) a scatter of 2 orders of magnitude in the possible stress drops (between 1 and 100 MPa) of the events, and (3) a cumulative coseismic slip of the order of 10 cm.…”

“…The characteristics can be summarized as follows: (1) a succession of 56 events with magnitudes ranging between 1.1 and 2.9 ruptured patches (asperities) within a 1 km long planar structure dipping approximately at 30° to the north and situated on the western edge of the inferred rupture plane of the 1995 M w 6.2 Aigion earthquake [ Bernard et al , ; Godano et al , ], (2) a scatter of 2 orders of magnitude in the possible stress drops (between 1 and 100 MPa) of the events, and (3) a cumulative coseismic slip of the order of 10 cm. The Bayesian inversion of the spectral ratios conducted by Godano et al [] allowed to estimate probability density functions for all the source parameters of these events. The results presented in Figures d and e were obtained by resampling all these probability density functions and therefore rigorously account for all the uncertainties associated with the source parameter estimation.…”

Identification of seismic doublets occurred on Rudna mine, Poland

“…Such conditions might have a direct physical interpretation and the most popular is that similar earthquakes occurred on the same part of fault by rerupturing of the same asperity at a different time. This simple concept provides a lot of possibilities to improve seismological studies, from the new events' location procedures up to new conceptual source models (e.g., Poupinet et al 1984;Got et al 1994;Waldhauser and Ellsworth 2000;Anooshehpoor and Brune 2001;Schaff and Waldhauser 2005;Baisch et al 2008;Rudziński and Dębski 2011;Spottiswoode and Milev 1998;Godano et al 2015).…”