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Start of funding 01.01.2011
Temporal earthquake reconstruction using luminescence dating techniques
Dr. Markus Fuchs
University of Bayreuth
Prof. Thomas K. Rockwell
San Diego State University
Department of Geological Sciences
Earthquakes represent a major natural hazard worldwide. In the field of earthquake risk assessment, the knowledge about the temporal occurrence of earthquakes is of fundamental importance. These investigations are generally based on evaluating the recurrence interval of earthquakes at a certain fault, analysing the sedimentary record of historical surface ruptures. Optical stimulated luminescence (OSL) dating techniques offer the possibility to temporal determine former earthquakes. However, it is not clear if pressure is able to reset the luminescence signal of associated sediments during the occurrence of an earthquake. To test the potential of OSL sediment dating for paleoearthquake reconstruction samples from specific fault zones in California will be analysed and tested. This includes also tests at the Bavarian Research Institute of Geochemistry and Geophysics, which offers a worldwide unique cylinder press.
Final report:
The investigations were concentrated on two sites in California, the Imperial Fault System (IFS) east of San Diego in southern California, and the Camarillo Fold Belt (CFB) in the vicinity of Santa Barbara, southern California. At the IFS, seven (7) sediment samples were taken for optical stimulating luminescence dating (OSL), from the CFB 14 samples were taken for OSL and IRSL (infrared stimulated luminescence) dating. The samples represent colluvial and alluvial sediments and can be related to young Quaternary fault activity of the nearby fault systems. All samples were prepared and analyzed in the luminescence laboratory of the University of Bayreuth.
First results demonstrate the potential of luminescence dating for reconstructing past fault activity and therefore dating historic earthquakes. The results clearly show that successful dating of fault-related sediments depends on the identification of sediments, which were transported and deposited as colluvial and / or alluvial material. This geomorphic process allows the resetting of the luminescence signal and therefore the dating of the fault activity. Sediments, which were not transported and bleached, showed luminescence ages older than expected. Pressure caused by fault activity might not be adequate or strong enough to reset the luminescence signal. However, these investigations are still in progress and final statements of the influence of pressure on the resetting of the luminescence signal cannot be made up to now.
In the future, the US and German laboratories will continue their successful cooperation in the field of luminescence dating of sediments for reconstructing fault activity and earthquakes. The success of the cooperation is already expressed in e.g. two peer-reviewed publications in Lithosphere 2012.