OBSERVATORY Experiment Set-Up and Data Processing
In order to monitor micro seismicity at the Atacama and West Fissure Fault System (AF and WF) in Northern Chile, we installed two temporary seismic networks in March 2010. The net around the West Fissure Fault System was already operated during the periode 2005 to 2009.
Key targets are (I) to monitor the micro seismic activity related to the segment of the AF and WF near 21°S in time and space and (II) to understand the processes occurring in the fault zone. This requires the application of high-resolution earthquake location algorithms, detailed studies of source parameters and of the stress field. We also plan the reprocessing of active seismic data (ANCORP profile) and a combined interpretation of both passive and active seismic data.
The seismic monitoring system around the West Fissure Fault System covers an area of approx. 100 times 80km at elevations between 3000m and 5000m a.s.l. and consists of average 11 surface stations with 3-component seismometers of type Mark L4-1Hz (see Figures 1 and 2). The data recording is continuous at a sample rate of 200Hz. Data loggers are Earth Data PR-24. Power is supplied by a solar panel with a 12V battery backup.
The seismic monitoring system around the Atacama Fault System covers an area of approx. 40 times 30km at elevations between 600m and 1000m a.s.l. and consists of on 10 surface stations, instrumentation is the same as in the WF net.
Seismicity (Overview)
During the first two years (2005-2007), about 500 local seismic events with magnitudes -0.5 < ML<4.2 and focal depths between 2km and 50km have been located (Figure 3).
We observe crustal micro seismicity, which is only partly associated with known branches of the West Fissure Fault System. Among the seismic activity, two seismic clusters were detected, one at 35-40km depth in the SE of the monitoring area, and one in the central part at 9-10km depth beneath sea level. We currently work on the relocation of the events including cluster and multiplet analyis, and on the moment tensor and stress inversion of subsets of events.
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