## Retrieval of source parameters of an event of the 2000 West
Bohemia earthquake swarm assuming an anisotropic crust

**Dirk Rössler**,
**Frank Krüger**,
**Ivan Psencik**
&
**Georg Rümpker**
### Summary

We propose an inversion scheme to retrieve characteristics of seismic point sources, which
in contrast to common practice, takes into account anisotropy. If anisotropy is neglected durig
inversion, the moment tensors retrieved from seismic waves due to sources situated in anisotropic
media may be biased. Instead of the moment tensor, the geometry of the source is retrieved
directly in our inversion; if necessary, the moment tensor can be then determined from the
source geometry. The source geometry is defined by the orientation of the slip vector and the
fault normal as well as the strength of the event given by the size of the slip and the area of the
fault. This approach allows direct interpretation of the source geometry in terms of shear and
tensile faulting. It also makes possible to identify volumetric source changes that occur during
rupturing.
We apply the described algorithm to one event of the year 2000 earthquake swarm episode
in West Bohemia (Central Europe). For inversion we use information of the direct P waves.
The structure is approximated by three different models determined from travel-time observations.
The models are inhomogeneous isotropic, inhomogeneous anisotropic, and homogeneous
anisotropic. For these models we obtain seismic moments
M_{T} = 3.2 - 3.8 * 10^{14} Nm and leftlateral
near-vertical oblique normal faulting on a N-S trending rupture surface. The rupture
surface is consistent with fault-plane solutions of earlier studies and with the spatial distribution
of other events during this swarm. The event seems to be accompanied by a small amount
of crack opening. The amount of crack opening is slightly reduced when the inhomogeneous
anisotropic model is assumed, but it persists. This result seems to indicate a role of fluids on
the triggering of this event.

### Keywords

Seismic source, tensile earthquake, anisotropy, West Bohemia.

### Whole paper

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In: Seismic Waves in Complex 3-D Structures, Report 16,
pp. 283-306, Dep. Geophys., Charles Univ., Prague, 2006.

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