Investigation of ULF magnetic pulsations, air conductivity changes, and infra red signatures associated with the 30 October Alum Rock M5.4 earthquake
T. Bleier
1 , C. Dunson
1 , M. Maniscalco
1 , N. Bryant
2 , R. Bambery
2 , and F. Freund
31 QuakeFinder Inc., Palo Alto, California 94306, USA
2 NASA Jet Propulsion Laboratory (JPL), Pasadena, California 91109, USA
3 NASA Ames Research Center, Moffett Field, California 94035, USA
Received: 11 September 2008 – Revised: 9 March 2009 – Accepted: 11 March 2009 – Published: 16 April 2009
Abstract. Several electromagnetic signal types were ob-
served prior to and immediately after 30 October 2007 (Lo-
cal Time) M5.4 earthquake at Alum Rock, Ca with an epi-
center ∼15 km NE of San Jose Ca. The area where this
event occurred had been monitored since November 2005
by a QuakeFinder magnetometer site, unit 609, 2 km from
the epicenter. This instrument is one of 53 stations of
the QuakeFinder (QF) California Magnetometer Network-
CalMagNet. This station included an ultra low frequency
(ULF) 3-axis induction magnetometer, a simple air conduc-
tivity sensor to measure relative airborne ion concentrations,
and a geophone to identify the arrival of the P-wave from
an earthquake. Similar in frequency content to the increased
ULF activity reported two weeks prior to the Loma Prieta
M7.0 quake in 1989 (Fraser-Smith, 1990, 1991), the QF sta-
tion detected activity in the 0.01–12 Hz bands, but it con-
sisted of an increasing number of short duration (1 to 30 s
duration) pulsations. The pulsations peaked around 13 days
prior to the event. The amplitudes of the pulses were strong,
(3–20 nT), compared to the average ambient noise at the site,
(10–250 pT), which included a component arising from the
Bay Area Rapid Transit (BART) operations. The QF station
also detected different pulse shapes, e.g. negative or posi-
tive only polarity, with some pulses including a combination
of positive and negative. Typical pulse counts over the pre-
vious year ranged from 0–15 per day, while the count rose
to 176 (east-west channel) on 17 October, 13 days prior to
the quake. The air conductivity sensor saturated for over
14 h during the night and morning prior to the quake, which
occurred at 20:29 LT. Anomalous IR signatures were also
observed in the general area, within 50 km of the epicenter,
during the 2 weeks prior to the quake. These three simultane-
ous EM phenomena were compared with data collected over
a 1–2-year period at the site. The data was also compared
against accounts of air ionization reported to be associated
with radon emission from the ground (Ouzounov, 2007), and
a series of laboratory rock stressing experiments (Freund,
2006, 2007a, b, c) to determine if field data was consistent ei-
ther of these accounts. We could not find a data set with pre-
earthquake radon measurements taken near the Alum Rock
epicenter to compare against our field data. However, based
on the Alum Rock data set example and another data set at
Parkfield, the field tests are at least consistent with the lab ex-
periments showing currents, magnetic field disturbances, air
conductivity changes, and IR signatures. This is encourag-
ing, but more instrumented earthquake examples are needed
to prove a repeating pattern for these types of pre-earthquake
EM signatures.
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