Earthquake Lights and Electric Ground Potentials Following the South Napa Earthquake

Friedemann T. Freund1,2, John Scoville3, Jorge Arturo Heraud4, Stevan Spremo5, Jaufray Sornette3, Paul Kosovich6 and Oliwia N Baney7, (1)NASA Ames Research Center, Moffett Field, United States, (2)SETI Institute, Carl Sagan Center, Mountain View, United States, (3)SETI Institute Mountain View, Mountain View, CA, United States, (4)Pontificia Universidad Catolica del Peru, LIMA, Peru, (5)NASA Ames Research Center, Moffett Field, CA, United States, (6)SETI Institute Mountain View, Mountain View, United States, (7)University of California Los Angeles, Los Angeles, CA, United States
Abstract:
Earthquake lights (EQLs) in form of bright flashes have been documented multiple times by private security cameras during and after the M6.0 South Napa earthquake of Aug. 24, 2014. On the video records, series of flashes are seen rising out of the ground, sometimes in rapid succession, at other times as single events brightly illuminating the night sky. The EQLs appear to come from extended sources, probably up to hundreds of meters in lateral extent. Though few video records display accurate GPS-timing, most of the flashes were clearly co-seismic in the sense that they coincided with the local arrival of the seismic waves.

This pattern is consistent with records obtained by a surveillance camera and a seismometer co-located on the PUCP campus in Lima, Peru, during the arrival of the P and S waves from the M8.0 Pisco earthquake about 150 km to the southeast of Lima. Analysis of the PUCP and other video records, plus a number of eyewitness reports, indicate that the EQLs were associated (i) with the S waves and (ii) with mafic dykes.

Attempts to see to detect the Napa EQLs on records of the GOES satellite were unsuccessful.

Unusual conditions have to exist to produce electric discharges at the Earth's surface that can rise 100-200 m into the sky. Key to understanding the underlying processes is the fact that, when mafic rocks are stressed, positive hole charge carriers become activated, i.e. defect electrons in the oxygen anion sublattice. The higher the stress rate, the higher the currents, reaching currents on the order of 1-2 billion A/km3 during compaction of gabbro within 1-2 msec. Obviously, when S waves pass through rocks at velocities around 3.4 km/sec, large numbers of positive holes appear. Flowing out of the stressed rock volume they can create very high electric fields, leading to a number of follow-on processes including corona discharges. In Campbell near San Jose, about 60 km south of Napa, a security camera, motion-triggered by the arrival of the seismic waves, recorded electric arcs coming out of an unused power cord hanging off the eve of a private residence. The arc started to spark about 30 sec after the camera was triggered, bridging an air gap of 2.5-5 cm and continuing for at least 90 sec, suggesting up 100 kV.

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