Fast Kinematic Waveform Inversion and Robustness Analysis: Application to the 2007 Mw 5.9 Horseshoe Abyssal Plain Earthquake Offshore Southwest Iberia

Abstract

An M w 5.9 earthquake occurred beneath the Horseshoe abyssal plain (HAP), offshore southwest Iberia, on 12 February 2007. The region where the earthquake occurred has a high seismogenic and tsunamigenic potential. The purpose of this paper is twofold: (1) to extract information about the source of the earthquake that contributes to the understanding of regional tectonics; and (2) to evaluate the applicability of a fast algorithm to study a moderate earthquake offshore mainland Portugal. We employed the KIWI tools, which implement a multistep inversion algorithm, to infer both the point‐ and finite‐source properties of the earthquake. In order to assess the robustness of our solutions, we performed independent sets of inversions that take different datasets and assumptions (e.g., Green’s functions, passbands, wave types) as inputs. We also performed bootstrap analyses in order to appraise the robustness of the source parameters. We concluded that the 2007 HAP earthquake centroid is located at 35.841° N, 10.611° W, at a depth of 39 km. Scalar moment, M , is consistently retrieved with an average value of ![Graphic][1] (moment magnitude M w 5.9). The finite‐fault parameters are difficult to resolve given the existing data. Approximately 70% of our bootstrap solutions indicate a true rupture plane that trends west‐northwest–east‐southeast (strike=128°, dip=46°, and rake=138°). The location and strike of this fault plane coincide with the southwest Iberian margin (SWIM) faults. However, the 46° dip is difficult to reconcile with the subvertical nature of the SWIM faults. Online Material: Inversion results using teleseismic data, PREM, and body waves only. [1]: /embed/inline-graphic-1.gif