Abstract

We collected analog seismogram recordings and seismic bulletins for two moderate magnitude earthquakes in the province of Jaén, southern Spain, on 10 March and 19 May 1951, and the series of aftershocks. Seismograms from the two main events reveal striking similarity, pointing to nearby locations and similar source mechanisms. This casts a shadow on the quality of preserved phase readings and macroseismic data, which suggests a distance of several tens of kilometers between both mainshocks and aftershocks. A critical review of available phase readings permitted us to detect several misinterpretations in the original bulletins and to obtain better constrained hypocenter relocations—about 10 km apart—for the two mainshocks, as well as location estimates for 20 aftershocks. The recording of the 1951 Jaén earthquake doublet at a network of common stations allows a straightforward quality control of our digitized seismograms by waveform comparison. We estimate faulting parameters of the two mainshocks from regional moment tensor inversion, obtaining moment magnitude Mw 5:2 and Mw 5:3, respectively, depth of 20 km, and strike-slip faulting mechanisms with minor normal slip component and northeast– southwest oriented T axes. Deconvolution of body waveforms from an Mw 4:4 aftershock yields simple triangular source time functions for both main events, with durations close to 1 sec. While several previous studies had difficulties in characterizing these earthquakes, partially describing them as unusual intermediate deep focus events, we propose simple shear faulting sources in the middle crust and faulting geometries consistent with the regional seismotectonic framework.

Online Material: Phase arrival times, seismograph constants for deconvolution, and color plots of probability density functions.