Abstract
The Lorca earthquake (May 11th, 2011, Mw 5.2) stands as the most destructive one in Spain over the last 50 years, interpreted as having occurred in an intersegment zone of the strike–slip Alhama de Murcia Fault (AMF) (Eastern Betics, Spain). Magnetotelluric data were acquired along a profile to the SW of Lorca (La Torrecilla profile), to characterize its signature at depth, as part of the multidisciplinary project “INTERGEOSIMA”. Given the short distance between stations, some station pairs were recorded simultaneously, with magnetic sensors in only one of them. In order to properly understand the resulting impedances (called interstation impedances), and the effects of inverting them, we used synthetic models to compare the impedances and the interstation impedances and to analyze the corresponding inversion results, together with the inversion of the quasi-impedance (inversion of the interstation impedances, considering them as impedances). The results are sensitive to the location of the magnetic sensors and the resistivity underneath, but in general the use of the quasi-impedances in the inversion can be considered a valid procedure. Both the 2D and the 3D resistivity models obtained through the inversion allowed us to complement the previous ERT models and represent the continuation of the main fault gouge in depth showing its extension towards the SE.
Highlights
The Alhama de Murcia Fault (AMF) is an 87-km-long, SW–NE oriented left-lateral strike–slip fault located in the southeast of the Iberian Peninsula
With the aim of better understanding the interstation impedances and the effects of inverting them for the Torrecilla profile, in the first part of the paper we present the results from synthetic tests using interstation impedance (ZI), which was implemented into the ModEM code (Egbert and Kelbert 2012; Kelbert et al 2014) to identify the differences between the Z and Interstation impedance tensor (ZI) responses; and the effects of inverting Z, ZI or Quasi-impedance tensor (qZ)
We carried out a magnetotelluric study for the Góñar– Lorca sector of the Alhama de Murcia Fault in order to reveal its structure at depth
Summary
The Alhama de Murcia Fault (AMF) is an 87-km-long, SW–NE oriented left-lateral strike–slip fault located in the southeast of the Iberian Peninsula. We carried out the MT survey in La Torrecilla (Góñar–Lorca segment), in order to better constrain this interpretation and to obtain more information on the structure of the basement, such as to determine the actual width of the shear zone and the possibility of the existence of other blind branches or faults beneath the Quaternary sediments This survey was co-located with the previous ERT and seismic profiles Regarding C1, we modified its resistivity to 50 Ω·m and to 200 Ω·m and run the forward problem for each case, leading to rms values of 3.5 and 3.8, respectively, and to a poor fit between the data and model responses—especially for sites located just above the conductor C1 (see Additional file 2: Figure S2-4) Both tests confirm that both the Upper C–R and C1 structures are required by the model in order to fit the data.
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