Frictional heating during coseismic deformation can lead to the melting of the fault rocks and formation of pseudotachylite if slip is important. The increasingly reported existence of earthquake lightning shows that transient coseismic electric currents of large intensity are associated with large magnitude earthquakes (M > 6.0). Such currents are likely to follow pseudotachylite veins because their electric conductivity, being melts, is considerably larger than that of the unmolten rocks. All previous and preliminary results on fault-related pseudotachylites show that they have an anomalously high remanent magnetization. Their remanent magnetic properties are similar to those of lightning struck rocks, which suggests that large electric pulses were involved in the magnetization. This project aims at demonstrating that remanence anomalies in pseudotachylites are generally observed and that coseismic electric currents are responsible for it. The investigators propose to test the hypothesis on three young pseudotachylites from seismically active fault zones (California, Japan and Western Alps) by collecting oriented samples for paleomagnetic studies. Samples collected at various points with respect to the main fault plane will enable us to test the coseismic current hypothesis. The geometry and the characteristics of the magnetizing field will be compared with the Earth's magnetic field at the time of pseudotachylite formation. This will provide an independent second test for the coseismic current hypothesis. A series of experiments will generate artificial pseudotachylites using the friction welding method. The artificial and natural pseudotachylites will be compared to assess the possible causes of anomalous magnetization in natural specimens. The direct study of coseismic currents is made difficult by their transient nature. This problem can be circumvented by using the remanent magnetic record of rocks affected by the electrical phenomenon. This research will open new directions of investigation on coseismic electric currents in fault rocks and should contribute to a better understanding of coseismic electric phenomena --

Agency
National Science Foundation (NSF)
Institute
Division of Earth Sciences (EAR)
Type
Standard Grant (Standard)
Application #
0228818
Program Officer
Robin Reichlin
Project Start
Project End
Budget Start
2003-01-01
Budget End
2004-12-31
Support Year
Fiscal Year
2002
Total Cost
$110,452
Indirect Cost
Name
Southern Illinois University at Carbondale
Department
Type
DUNS #
City
Carbondale
State
IL
Country
United States
Zip Code
62901