Static stress changes due to the 1998 and 2004 Krn Mountain (Slovenia) earthquakes and implications for future seismicity

A Ganas,A Gosar,G Drakatos

doi:10.5194/nhess-8-59-2008

Abstract

Abstract. In this paper we examine the Coulomb (static) stress pattern following the two moderate magnitude earthquakes in NW Slovenia during 1998 and 2004. These earthquakes ruptured patches of the NW-SE striking Ravne fault that crosses the Krn Mountain. The objective is to investigate the seismicity patterns for this area of Slovenia given that future earthquakes may be triggered as a result of stress changes along neighbouring faults. Our findings include: a) stress levels have increased along the active Ravne fault for all models discussed b) stress levels have decreased along the active, NW-SE striking Idrija fault and c) stress levels throughout the crust have increased along the E-W direction but have decreased in the N-S direction (stress shadow effect). We also mapped a better correlation of the off-fault aftershock locations with stress maps incorporating the regional stress field.

Highlights

Our findings include: a) stress levels have increased along the active Ravne fault for all models discussed b) stress levels have decreased along the active, NW-SE striking Idrija fault and c) stress levels throughout the crust have increased along the E-W direction but have decreased in the N-S direction
In the last ten years, western Slovenia was struck by two strong earthquakes
Our calculations show the effects of the combined Coulomb stress change in this region of Slovenia, including the location of stress shadows

Summary

Introduction

The first event occurred on 12 April 1998 at 10:55 UTC with a moment magnitude of 5.6. The total seismic moment was 4.5×1017 Nm (1024 dyn-cm) implying an average, co-seismic slip of 0.18 m (Bajc et al, 2001). A second earthquake (Mw=5.2) occurred on 12 July 2004 at 13:04 UTC to the northwest of the epicentre of the 1998 event (Fig. 1). Both events show right-lateral, strike-slip kinematics (Fig. 1; Bajc et al, 2001; Kastelic et al, 2006). In this paper we investigate a) the static stress change following the 1998 event

Active tectonics and seismicity

Method

Stress changes on the active faults

Stress changes on optimally oriented faults to the regional stress field