Abstract
AbstractPhyllosilicate‐rich rocks which commonly occur within fault zones cause seismic velocity anisotropy. However, anisotropy is not always taken into account in seismic imaging and the extent of the anisotropy is often unknown. Laboratory measurements of the velocity anisotropy of fault zone rocks and gouge from the Carboneras fault zone in SE Spain indicate 10–15% velocity anisotropy in the gouge and 35–50% anisotropy in the mica‐schist protolith. Greater differences in velocity are observed between the fast and slow directions in the mica‐schist rock than between the gouge and the slow direction of the rock. This implies that the orientation of the anisotropy with respect to the fault is key in imaging the fault seismically. For example, for fault‐parallel anisotropy, a significantly greater velocity contrast between fault gouge and rock will occur along the fault than across it, highlighting the importance of considering the foliation orientation in design of seismic experiments.
Highlights
Identifying faults is an important step toward understanding fault mechanics and is crucial in accurately and reliably assessing seismic hazard
Phyllosilicate-rich rocks which commonly occur within fault zones cause seismic velocity anisotropy
Faults are identified in seismic refraction surveys from vertical offsets in velocity profiles and distinctive features in the seismic arrivals caused by low velocities, velocity contrasts across the fault and fault zone head waves [e.g., Yan et al, 2005]
Summary
Identifying faults is an important step toward understanding fault mechanics and is crucial in accurately and reliably assessing seismic hazard. Seismic investigations are often conducted in order to understand the fault structure at depth. Tomographic studies can image the area around a fault zone [e.g., Thurber et al, 2006] and may indicate the extent of fracturing and damage [e.g., Lin and Shearer, 2009]. Narrow structures such as individual fault strands may not be resolved. The imaging resolution may be improved by adding travel time information of phases that spend much of their travel path along the fault zone structure [e.g., Ben-Zion et al, 1992]
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