Waveform inversion of small-to-moderate earthquakes located offshore southwest Iberia

In this paper we apply the KInematic Waveform Inversion (KIWI) tools to the study of small-to-moderate earthquakes in southwest (SW) Iberia. The earthquakes have magnitudes in the range M-L 3.5-4.9, with the exception of one earthquake with magnitude M-L 6.0. Most events are located offshore, are recorded with a large azimuthal gap and generate waves that travel through a strongly heterogeneous crustal structure. We obtain new estimates of centroid, depth, seismic moment, strike, dip and rake for 12 of the 29 studied events. The earthquakes whose waveforms we cannot successfully model are (1) located too far from the stations, (2) have small magnitude, hence low signal-to-noise ratio or (3) are located within the Cadiz basin, which is a major sedimentary basin that affects wave propagation notably. Our results indicate that onshore earthquakes occur at shallow depths (<15 km), whereas offshore earthquakes occur deeper, down to 46 km. Focal mechanisms indicate transpressive faulting.