Crustal structure of the Betic–Rif system, western Mediterranean, from local earthquake tomography

Moudnib, Lahcen El; Villaseñor, Antonio; Harnafi, M.; Muset, Josep Gallart; Pazos, Antonio; Serrano, Inmaculada; Córdoba, Diego; Pulgar, J. A.; Ibarra, P.; Himmi, Mohammed Majid; Chourak, Mimoun

doi:10.1016/j.tecto.2014.12.015

Cited by 27 publications

(30 citation statements)

References 37 publications

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“…Seismic velocities derived from the inversion procedure indicates upper and lower crustal velocities of ~6.2 km/s and ~6.6 km/s, respectively. Crustal velocities of <7 km/s are supported by local earthquake tomography for the Alboran domain [ El Moudnib et al ., ]. Thus, velocities range indeed within the values expected for continental crust [ Christensen and Mooney , ] rather than indicating typical arc‐like crust with seismic velocities of the lower crust of 7 km/s or faster [e.g., Contreras‐Reyes et al ., ].…”

Section: Discussionsupporting

confidence: 78%

“…El Moudnib et al . [] suggested that the higher velocities may correspond to a mechanically stronger block stretching across the Alboran Sea and may coincide with rocks of an immature volcanic arc or magmatic intrusions associated with Miocene arc volcanism [ Duggen et al ., ].…”

Section: Discussionmentioning

confidence: 55%

“…Structurally, the Trans‐Alboran Shear Zone is associated with faster P wave velocity than rocks to the west and east, most clearly between 8 and 24 km depth [ El Moudnib et al ., ]. El Moudnib et al .…”

Section: Discussionmentioning

confidence: 99%

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Seismicity and active tectonics in the Alboran Sea, Western Mediterranean: Constraints from an offshore‐onshore seismological network and swath bathymetry data

et al. 2015

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Seismicity and tectonic structure of the Alboran Sea were derived from a large amphibious seismological network deployed in the offshore basins and onshore in Spain and Morocco, an area where the convergence between the African and Eurasian plates causes distributed deformation. Crustal structure derived from local earthquake data suggests that the Alboran Sea is underlain by thinned continental crust with a mean thickness of about 20 km. During the 5 months of offshore network operation, a total of 229 local earthquakes were located within the Alboran Sea and neighboring areas. Earthquakes were generally crustal events, and in the offshore domain, most of them occurred at crustal levels of 2 to 15 km depth. Earthquakes in the Alboran Sea are poorly related to large‐scale tectonic features and form a 20 to 40 km wide NNE‐SSW trending belt of seismicity between Adra (Spain) and Al Hoceima (Morocco), supporting the case for a major left‐lateral shear zone across the Alboran Sea. Such a shear zone is in accord with high‐resolution bathymetric data and seismic reflection imaging, indicating a number of small active fault zones, some of which offset the seafloor, rather than supporting a well‐defined discrete plate boundary fault. Moreover, a number of large faults known to be active as evidenced from bathymetry, seismic reflection, and paleoseismic data such as the Yusuf and Carboneras faults were seismically inactive. Earthquakes below the Western Alboran Basin occurred at 70 to 110 km depth and hence reflected intermediate depth seismicity related to subducted lithosphere.

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Section: Discussionsupporting

confidence: 78%

Section: Discussionmentioning

confidence: 55%

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Seismicity and active tectonics in the Alboran Sea, Western Mediterranean: Constraints from an offshore‐onshore seismological network and swath bathymetry data

et al. 2015

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“…Similar S velocity variations on the order of ±10 % over similar distances were found in tomographic studies of other regions, including the Iberian Peninsula (e.g. El Moudnib et al, 2015;Fichtner and Villaseñor , 2015), California (e.g. Shapiro et al, 2005;Tape et al, 2010), the Caribbean plate (e.g.…”

Section: Random Models Of Plausible Earth Structuresupporting

confidence: 79%

The imprint of crustal density heterogeneities on regional seismic wave propagation

2016

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Abstract. Density heterogeneities are the source of mass transport in the Earth. However, the 3-D density structure remains poorly constrained because travel times of seismic waves are only weakly sensitive to density. Inspired by recent developments in seismic waveform tomography, we investigate whether the visibility of 3-D density heterogeneities may be improved by inverting not only travel times of specific seismic phases but complete seismograms.As a first step in this direction, we perform numerical experiments to estimate the effect of 3-D crustal density heterogeneities on regional seismic wave propagation. While a finite number of numerical experiments may not capture the full range of possible scenarios, our results still indicate that realistic crustal density variations may lead to travel-time shifts of up to ∼ 1 s and amplitude variations of several tens of percent over propagation distances of ∼ 1000 km. Both amplitude and travel-time variations increase with increasing epicentral distance and increasing medium complexity, i.e. decreasing correlation length of the heterogeneities. They are practically negligible when the correlation length of the heterogeneities is much larger than the wavelength. However, when the correlation length approaches the wavelength, density-induced waveform perturbations become prominent. Recent regional-scale full-waveform inversions that resolve structure at the scale of a wavelength already reach this regime.Our numerical experiments suggest that waveform perturbations induced by realistic crustal density variations can be observed in high-quality regional seismic data. While density-induced travel-time differences will often be small, amplitude variations exceeding ±10 % are comparable to those induced by 3-D velocity structure and attenuation.While these results certainly encourage more research on the development of 3-D density tomography, they also suggest that current full-waveform inversions that use amplitude information may be biased due to the neglect of 3-D variations in density.

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“…(a) Epicenters considering a standard velocity model. (b) Relocated epicenters for the highest‐magnitude earthquakes of the 2016–2017 seismic sequence according to El Moudnib et al (). Legend: FP, Francesc Pagès seamount; NB, Nekor Basin.…”

Section: Introductionmentioning

confidence: 99%

Imaging the Growth of Recent Faults: The Case of 2016–2017 Seismic Sequence Sea Bottom Deformation in the Alboran Sea (Western Mediterranean)

et al. 2018

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The Eurasian-African NW-SE oblique plate convergence produces shortening and orthogonal extension in the Alboran Sea Basin (westernmost Mediterranean), located between the Betic and Rif Cordilleras. A NNE-SSW broadband of deformation and seismicity affects the Alboran central part. After the 1993-1994 and 2004 seismic series, an earthquake sequence struck mainly its southern sector in 2016-2017 (main event M w = 6.3, 25 January 2016). The near-surface deformation is investigated using seismic profiles, multibeam bathymetry, gravity and seismicity data. Epicenters can be grouped into two main alignments. The northern WSW-ENE alignment has reverse earthquake focal mechanisms, and in its epicentral region recent mass transport deposits occur. The southern alignment consists of a NNE-SSW vertical sinistral deformation zone, with early epicenters of higher-magnitude earthquakes located along a narrow band 5 to 10-km offset westward of the Al Idrisi Fault. Here near-surface deformation includes active NW-SE vertical and normal faults, unmapped until now. Later, epicenters spread eastward, reaching the Al Idrisi Fault, characterized by discontinuous active NNE-SSW vertical fractures. Seismicity and tectonic structures suggest a westward propagation of deformation and the growth at depth of incipient faults, comprising a NNE-SSW sinistral fault zone in depth that is connected upward with NW-SE vertical and normal faults. This recent fault zone is segmented and responsible for the seismicity in 1993-1994 in the coastal area, in 2004 onshore, and in 2016-2017 offshore. Insights for seismic hazard assessment point to the growth of recent faults that could produce potentially higher magnitude earthquakes than the already formed faults.

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Crustal structure of the Betic–Rif system, western Mediterranean, from local earthquake tomography

Cited by 27 publications

References 37 publications

Seismicity and active tectonics in the Alboran Sea, Western Mediterranean: Constraints from an offshore‐onshore seismological network and swath bathymetry data

Seismicity and active tectonics in the Alboran Sea, Western Mediterranean: Constraints from an offshore‐onshore seismological network and swath bathymetry data

The imprint of crustal density heterogeneities on regional seismic wave propagation

Imaging the Growth of Recent Faults: The Case of 2016–2017 Seismic Sequence Sea Bottom Deformation in the Alboran Sea (Western Mediterranean)

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