Abstract
AbstractThe magnetotelluric method has been used to image the deep electrical structure of the Remiremont-Epinal-Rambervillers region in the French Vosges Massif, which has presented a significant seismic activity in the past decades. Several earthquakes of moderate magnitude (up to 5.1) occurred in this area with a systematic migration along a nearly N-S direction. Inversion of the magnetotelluric data reveals zones of high electrical conductivity. A large conductive body presents a significative spatial correlation with the region that was most recently affected by earthquakes. This conductive body is interpreted as a consequence of the presence of a fluid filled basement fault network in proximity to the zone affected by the last seismic crisis, where fluid pressure diffusion takes place for several years after the main shock and participates in maintaining a microseismic activity.
Highlights
Fluid flow and fluid pressure appear to play an important role in the dynamics of fault zones
High-pressure fluid migration has been proposed to explain the migration of aftershocks [Miller et al, 2004], or the overpressure found in accretionary wedge décollement several years after a large earthquake [Bourlange and Henry, 2007]
A series of recent magnetotelluric studies at the San Andreas fault (SAF) and other active areas imaged electrical conductivity anomalies in the crust which are related to earthquakes distribution [Becken et al, 2011; Yamaguchi et al, 2010; Wannamaker et al, 2010; Yoshimura et al, 2009; Brasse et al, 2009; Brasse and Eydam, 2008; Jiracek et al, 2007; Mekkawi and Saleh, 2007]
Summary
Fluid flow and fluid pressure appear to play an important role in the dynamics of fault zones. The presence of high-pressure fluids at depth could cause fault failure during the seismic cycle [Byerlee, 1993; Rice, 1992] It could play an important role in fault propagation and trigger shallow earthquakes [Mekkawi et al, 2003]. A series of recent magnetotelluric studies at the San Andreas fault (SAF) and other active areas imaged electrical conductivity anomalies in the crust which are related to earthquakes distribution [Becken et al, 2011; Yamaguchi et al, 2010; Wannamaker et al, 2010; Yoshimura et al, 2009; Brasse et al, 2009; Brasse and Eydam, 2008; Jiracek et al, 2007; Mekkawi and Saleh, 2007] They have suggested that these conductive anomalies could result from the presence of crustal fluids and/or ore minerals (e.g. graphite, salt, sulphides) accumulated in the fractures system. We present here the results of a magnetotelluric survey that was conducted in the Remiremont-Epinal-Rambervillers area in order to test the presence of fluids at depth in the region
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