The 2004 Parkfield earthquake: Test of the electromagnetic precursor hypothesis
Abstract
A controversy has existed for 30 years concerning the possibility of earthquake prediction using electromagnetic precursors. Long-term electromagnetic monitoring prior to, during, and after the M6.0 earthquake at Parkfield, California, on 28 September 2004 now provides a definitive test of this hypothesis. During the earthquake our instruments recorded clearly documented electrical signals from an earthquake: impulsive changes of up to +2.5 mV at an electrode located 250 m from the rupture zone followed by a transient decay lasting at least 3 1/4 hours. Similar signals (-1.5 mV) were recorded with the only two M > 5 aftershocks, but their transient decays lasted for only ∼17 min. These signals are unambiguously a result of the earthquake and can be useful in studies of fluid flow in faults, a major current topic in earthquake physics. Patterns in the distribution of transient voltages differ from static stress changes, but are consistent with a small coseismic pressure drop on the fault and fluid flow inward. Signals at a distance of 1 km from the fault are less than 1 mV and are statistically no different from zero in our analysis. Transient voltages for the aftershocks have opposite polarity from those recorded with the main shock and are again maximal close to the fault, suggesting subsequent outward flow from the fault. Finally, there is no evidence of any precursory signal, strongly calling into question previously suggested signals preceding smaller or more distant earthquakes.
- Publication:
-
Journal of Geophysical Research (Solid Earth)
- Pub Date:
- May 2007
- DOI:
- 10.1029/2005JB004196
- Bibcode:
- 2007JGRB..112.5302P
- Keywords:
-
- Seismology: Earthquake interaction;
- forecasting;
- and prediction (1217;
- 1242);
- Physical Properties of Rocks: Magnetic and electrical properties (0925);
- Geomagnetism and Paleomagnetism: Geomagnetic induction;
- Exploration Geophysics: Magnetic and electrical methods (5109);
- Parkfield;
- precursor;
- electromagnetic