Shallow Seismic Velocity Structure of the Betic Cordillera (Southern Spain) from Modelling of Rayleigh Wave Dispersion

Abstract

A detailed dispersion analysis of Rayleigh waves generated by local earthquakes and occasionally by blasts that occurred in southern Spain, was undertaken to obtain the shear-wave velocity structure of the region at shallow depth. Our database includes seismograms generated by 35 seismic events that were recorded by 15 single-component short-period stations from 1990 to 1995. All these events have focal depths less than 10 km and body-wave magnitudes between 3.0 and 4.0, and they were all recorded at distances between 40 and 300 km from the epicentre. We analysed a total of 90 source-station Rayleigh-wave paths. The collected data were processed by standard digital filtering techniques to obtain Rayleigh-wave group-velocity dispersion measurements. The path-averaged group velocities vary from 1.12 to 2.25 km/s within the 1.0-6.0 s period interval. Then, using a stochastic inversion approach we obtained 1-D shearwave velocity-depth models across the study area, which were resolved to a depth of circa 5 km. The inverted shear-wave velocities range approximately between 1.0 and 3.8 km/s with a standard deviation range of 0.05-0.16 km/s, and show significant variations from region to region. These results were combined to produce 3-D images via volumetric modelling and data visualization. We present images that show different shear velocity patterns for the Betic Cordillera. Looking at the velocity distribution at various depths and at vertical sections, we discuss of the study area in terms of subsurface structure and S-wave velocity distribution (low velocity channels, basement depth, etc.) at very shallow depths (0-5 km). Our results characterize the region sufficiently and lead to a correlation of shear-wave velocity with the different geological units features.

Shear-wave velocity structure of the south-eastern part of the Iberian Peninsula from Rayleigh wave analysis

“…This high velocity coincides with the high conductivity of External zone obtained from the Magnetotelluric data model (Pous et al 1999). This S-wave velocity agrees well with the results obtained from a previous surface wave analysis (Chourak et al 2005) and the results obtained from other geophysical data analysis (Carbonell et al 1998). It should be noted that the western part of Betic cordillera shows lower velocity values than the eastern part.…”

“…On the other hand, several S-wave velocity models of the Iberian area have been obtained for shallow depths (from 0 to 4 or 5 km of depth) from shortperiod Rayleigh waves (Sarrate et al 1993;Navarro et al 1997;Chourak et al 2003). A recent study, performed by Chourak et al (2005) for the south-eastern part of Iberia, also has the same depth range: from 0 to 4 km of depth. Thus, up to now and for the south-eastern Iberia, no S-velocity models have been obtained in the range of intermediate depths, from 4-5 to 24-30 km of depth.…”

Ambient noise surface wave tomography of the Iberian Peninsula: Implications for shallow seismic structure

“…Using two-station dispersion measurements, Corchete et al [1995] obtained shearwave images of the lithosphere and asthenosphere beneath the Iberian Peninsula. The shallow structure has also been studied using short period (1 -6 seconds) Rg Rayleigh waves from small earthquakes and explosions for different regions of Iberia (e.g., Chourak et al [2005] for the Betics).…”

Shear Wave Velocity Structure of the Sinai Peninsula from Rayleigh Wave Analysis

“…Considering the improvements related above, this filtering process is revealed as a powerful tool for dispersion analysis. For this reason, this filtering process is considered nowadays as a standard tool for dispersion analysis in long and short period (Corchete et al 1995;Chourak et al 2003Chourak et al , 2005.…”