Local and regional minimum 1D models for earthquake location and data quality assessment in complex tectonic regions: application to Switzerland

Abstract

One-dimensional (1D) velocity models are still widely used for computing earthquake locations at seismological centers or in regions where three-dimensional (3D) velocity models are not available due to the lack of data of sufficiently high quality. The concept of the minimum 1D model with appropriate station corrections provides a framework to compute initial hypocenter locations and seismic velocities for local earthquake tomography. Since a minimum 1D model represents a solution to the coupled hypocenter-velocity problem it also represents a suitable velocity model for earthquake location and data quality assessment, such as evaluating the consistency in assigning pre-defined weighting classes and average picking error. Nevertheless, the use of a simple 1D velocity structure in combination with station delays raises the question of how appropriate the minimum 1D model concept is when applied to complex tectonic regions with significant three-dimensional (3D) variations in seismic velocities. In this study we compute one regional minimum 1D model and three local minimum 1D models for selected subregions of the Swiss Alpine region, which exhibits a strongly varying Moho topography. We compare the regional and local minimum 1D models in terms of earthquake locations and data quality assessment to measure their performance. Our results show that the local minimum 1D models provide more realistic hypocenter locations and better data fits than a single model for the Alpine region. We attribute this to the fact that in a local minimum 1D model local and regional effects of the velocity structure can be better separated. Consequently, in tectonically complex regions, minimum 1D models should be computed in sub-regions defined by similar structure, if they are used for earthquake location and data quality assessment.

Noise-based monitoring and imaging of aseismic transient deformation induced by the 2006 Basel reservoir stimulation

“…We use the local velocity model of Deichmann and Ernst (2009). The sensitivity in the microseisms' frequency range (0.1-0.4 Hz) was confirmed using a regional model with poor resolution near the surface, but with better resolution below 3-km depth (Husen et al, 2011), noting that microseisms refers to large-amplitude noise excited by nonlinear ocean-wave interactions with the solid earth, in contrast to microseismicity, which means small earthquakes. The vertical motion for the borehole sensors was obtained from the three components oriented in the Galperin sensor configuration.…”

Ambient-noise tomography of the Greater Geneva Basin in a geothermal exploration context

“…6). We also present a comparison of the Humilly-2 well-log and 1D Swiss velocity model (Husen et al 2011) with V s from our retrieved model (Fig. 8b).…”

“…7. (b) Comparison of V s profiles at the Humilly-2 well location: V s profile from the retrieved model (blue dashed line), V s converted from well-logged V p values (black solid line), and V s converted from the V p values of the 1D Swiss model (Husen et al 2011) below 2.5 km depth (gray solid line). The conversion from V p to V s was done assuming a constant V p /V s ratio of 1.73.…”

1D Velocity Structure and Characteristics of Contemporary Local Seismicity around the Tehri Region, Garhwal Himalaya

“…Accurate estimation of the hypocenters of earthquakes is fundamental for characterization of seismicity, because space-time distribution of seismicity forms an important ingredient to assess seismic hazard of seismically active regions (e.g., Hutton et al, 2006;Husen et al, 2011). 1D velocity models have been traditionally adopted to compute hypocenter parameters at local, regional, and global scales because ray tracing is computationally easier and more efficient for 1D velocity models compared to 3D models.…”