One-Dimensional qP-Wave Velocity Model of the Upper Crust for the West Bohemia/Vogtland Earthquake Swarm Region |
| |
Authors: | J Malek J Horalek J Jansky |
| |
Affiliation: | (1) Institute of Rock Structure and Mechanics, Acad. Sci. Czech Republic, V Holesovickach 41, 182 09 Prague 8, Czech Republic;(2) Geophysical Institute, Acad. Sci. Czech Republic, Bocni II/1401, 141 31 Prague 4, Czech Republic;(3) Department of Geophysics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic |
| |
Abstract: | The western part of the Bohemian Massif (West Bohemia/Vogtland region) is characteristic in the relatively frequent recurrence
of intraplate earthquake swarms and in other manifestations of past-to-recent geodynamic activity. In this study we derived
1D anisotropic qP-wave model of the upper crust in the seismogenic West Bohemia/Vogtland region by means of joint inversion
of two independent data sets - travel times from controlled shots and arrival times from local earthquakes extracted from
the WEBNET seismograms. We derived also simple 1-D P-wave and S-wave isotropic models. Reasons for deriving these models were:
(a) only simplified crustal velocity models, homogeneous half-space or 1D isotropic layered models of this region, have been
derived up to now and (b) a significant effective anisotropy of the upper crust in the region which was indicated recently
by S-wave splitting. Both our anisotropic qP-wave and isotropic P-and S-wave velocity models are constrained by four layers
with the constant velocity gradient. Weak anisotropy for P-waves is assumed. The isotropic model is represented by 9 parameters
and the anisotropic one is represented by 24 parameters. A new robust and effective optimization algorithm - isometric algorithm
- was used for the joint inversion. A two-step inversion algorithm was used. During the first step the isotropic P- and S-wave
velocity model was derived. In the second step, it was used as a background model and the parameters of anisotropy were sought.
Our 1D models are adequate for the upper crust in the West Bohemia/Vogtland swarm region up to a depth of 15 km. The qP-wave
velocity model shows 5% anisotropy, the minimum velocity in the horizontal direction corresponds to an azimuth of 170°. The
isotropic model indicates the VP/VS ratio variation with depth. The difference between the hypocentre locations based on the derived isotropic and anisotropic
models was found to be several hundreds of meters. |
| |
Keywords: | West Bohemia/Vogtland region earthquake swarm anisotropy 1D velocity model inverse problem earthquake location |
本文献已被 SpringerLink 等数据库收录! |
|