3:00 PM - 4:00 PM
[S05-P-05] STUDY OF THE 7TH JULY, 1923, CANAL DE BERDUN EARTHQUAKE, IN THE PYRENEES FROM CONTEMPORARY SEISMOGRAMS AND BULLETINS
Seismicity rate in the Pyrenees can be considered moderate. Nevertheless, damaging earthquakes occurs in this region as it is well known from their historical seismicity records. Among them, the 7th July, 1923, known as Canal de Berdun earthquake, is probably the largest one, according to the moment magnitude Mw = 5.4 that we compute in this study. Its size and unique location among the large earthquakes in the Pyrenees, in the central, south part of the chain, make this event of great interest for a better definition of the regional seismicity. For this reason we decided to study its source from the analysis of the available contemporary seismograms and related documents.
After a throughout collection and selection, 20 records for this earthquake have been digitized and processed. They were obtained at 9 different European stations. The event has been relocated and its magnitudes recalculated. We further characterized the earthquake through time domain moment tensor inversion. We obtain appropriate fits to regional recordings filtered in an intermediate period band (20 s to 50 s) for a pure normal faulting source with strike parallel to the Pyrenees (N292E), dip of 66 degreesand rake angle of -88 degress. The best fitting depth is 8 km. While previous normal faulting events in the Pyrenees occurred close to the axial zone and the highest topographies, suggesting a relation of seismicity to postcollisional extension, the location of this important normal faulting event at the southern frontal thrust of the Pyrenees suggests that this interpretation may be too simplistic.
After a throughout collection and selection, 20 records for this earthquake have been digitized and processed. They were obtained at 9 different European stations. The event has been relocated and its magnitudes recalculated. We further characterized the earthquake through time domain moment tensor inversion. We obtain appropriate fits to regional recordings filtered in an intermediate period band (20 s to 50 s) for a pure normal faulting source with strike parallel to the Pyrenees (N292E), dip of 66 degreesand rake angle of -88 degress. The best fitting depth is 8 km. While previous normal faulting events in the Pyrenees occurred close to the axial zone and the highest topographies, suggesting a relation of seismicity to postcollisional extension, the location of this important normal faulting event at the southern frontal thrust of the Pyrenees suggests that this interpretation may be too simplistic.