Refining seismic parameters in low seismicity areas by 3D trenching: The Alhama de Murcia fault, SE Iberia

Abstract

Three-dimensional paleoseismology in strike-slip faults with slip rates less than 1 mm per year involves a great methodological challenge. We adapted 3D trenching to track buried channels offset by the Alhama de Murcia seismogenic left-lateral strike-slip fault (SE Iberia). A fault net slip of 0.9 ± 0.1 mm/yr was determined using statistical analysis of piercing lines for one buried channel, whose age is constrained between 15.2 ± 1.1 ka and 21.9-22.3 cal BP. This value is larger and more accurate than the previously published slip rates for this fault. The minimum number of five paleo-earthquakes identified since the deposition of dated layers suggests a maximum average recurrence interval of approximately 5 ka. The combination of both seismic parameters yields a maximum slip per event between 5.3 and 6.3 m. We show that accurately planned trenching strategies and data processing may be key to obtaining robust paleoseismic parameters in low seismicity areas.

Neogene Basin Inversion and Recent Slip Rate Distribution of the Northern Termination of the Alhama de Murcia Fault (Eastern Betic Shear Zone, SE Spain)

“…At the Lorca-Totana section (Figure 1b), a 0.9 ± 0.1-mm/yr net-slip rate is estimated recently (Ferrater et al, 2016). Thus, the slip rate is higher in Lorca-Totana section and seems to decrease toward the northern termination of the AMF.…”

“…They suggested a vertical slip rate of 0.04-0.35 mm/yr in the Lorca-Totana section and, using the orientation of slickensides on the fault plane observed in the trenches, estimated a 0.07-to 0.66-mm/yr net-slip rate for the last 30 kyr. Recently, a three-dimensional paleoseismic study in the same section (Ferrater et al, 2016) suggests a 0.9 ± 0.1 mm/yr net-slip rate for the last 20 kyr, which is a value significantly larger. Moreover, Ortuño et al (2012) estimated a net-slip rate of 0.16-0.24 mm/yr for the last 47-63 kyr based on several paleoseismic sites in the Góñar-Lorca section.…”

“…Tectonics AMF have been estimated so far through morphotectonic and paleoseismic studies, in many cases with great uncertainties associated (Ferrater et al, 2016(Ferrater et al, , 2017Martínez-Díaz et al, 2003;Masana et al, 2004;Ortuño et al, 2012). Martínez-Díaz (1998), Martínez-Díaz et al (2003), and Ortuño et al (2012) estimated lateral slip rates based on morphotectonic analysis of offset channels for the southern sections of the AMF (Góñar-Lorca and Lorca-Totana Fault sections; Figure 1b).…”

“…The lower right inset shows the regional location of the eastern Betics and the main convergence direction. (b) Segmentation of the Alhama de Murcia Fault from Martínez-Díaz, Bejar-Pizarro, et al (2012) and summary of available slip rates for the AMF (Ferrater et al, 2016(Ferrater et al, , 2017Martínez-Díaz et al, 2003;Masana et al, 2004;Ortuño et al, 2012;Silva et al, 2003). Fault traces from the Quaternary active faults database of Iberia v.3 (QAFI, IGME, 2015).…”

Magnetotelluric characterization of the Alhama de Murcia Fault (Eastern Betics, Spain) and study of magnetotelluric interstation impedance inversion

“…In the neotectonic period (the last 9 My) a NNW-SSE compressional stress field became dominant and the AMF behaved as a transpressional oblique-slip structure (Montenat 1990;Martínez-Díaz et al 2012a). According to results from morphotectonics, paleoseismic and geodesic studies, the AMF, together with the Palomares Fault, accommodates ~ 1.0 mm/year of the approximately 5 mm/year of convergence between the Nubian and Eurasian plates (Echeverría et al 2013;Ferrater et al 2016). The AMF is one of the largest faults of the Eastern Betics Shear Zone (Silva et al 1993), and the cause for an important number of damaging historical earthquakes that have occurred in this area.…”