TY  - JOUR
ID  - epos1936
UR  - http://doi.org/10.1029/92GL00359
IS  - 7
A1  - Guyoton, Fabrice
A1  - Grasso, Jean-Robert
A1  - Volant, Philippe
Y1  - 1992/04/03/
N2  - From 1982 to 1989, more than 520 local seismic events were recorded by a permanent network of 9 telemetered stations over an active gas field (Lacq, France). The geological data of 46 boreholes coupled to several tens of kilometers of seismic profiles, concentrated in a small volume of 15 × 15 × 10 km3, allow the development of a very precise velocity structure, exhibiting a dome geometry limited by faulted strips. The discretized velocity model includes almost 20000 blocks with 500 m × 500 m × 250 m minimum dimensions. A relocation technique using this a priori detailed 3D velocity model allows precise locations of induced earthquakes. 351 relocated hypocenters show that of the seismic activity concentrated on geometrical discontinuities of the local dome structure. The locations of seismic events are correlated with geomechanical layers of the structure. Spatial and temporal migration of seismic ruptures mimics the different permeability rings of the reservoir which are progressively depleted by gas extraction. Most of these events are at present confined close to major thrust planes which limit the dome structure laterally, and in depth onto preexisting faults in the basement below the gas field. The occurence of these deep clusters demonstrates that fluid manipulation in the sedimentary covers can activate preexisting basement faults. This result changes previous assessments of local seismic risk and provides new insights into fault mechanisms in areas with complex geological structure.
PB  - Geophysical Research Letters
JF  - Geophysical Research Letters
VL  - 19
SN  - 00948276
TI  - Interrelation between induced seismic instabilities and complex geological structure
SP  - 705
AV  - none
EP  - 708
ER  -