Unusual
Animal Behavior Before Earthquakes:
A Review of Possible
Sensory Mechanisms
RUTH
E. BUSKIRK[1],
CLIFF FROHLICH, AND GARY V. LATHAM
University of Texas at Austin, Marine Science Institute, Galveston, Texas 77550
To determine
whether reports of unusual animal behavior before earthquakes are plausible,
we have compared these reports with recent laboratory studies of animal
sensory thresholds. Our major conclusion is that some animals are much more
capable than humans of perceiving certain kinds of geophysical stimuli which
may precede earthquakes. These geophysical stimuli are seismic or acoustic
waves at low frequency (below 50 Hz), electric field changes, and olfactory
stimuli. For example, recent studies suggest that some birds and fish are more
sensitive than humans to sounds with frequencies below 40 Hz, and many animals
are exceptionally good at perceiving low-frequency vibrations through their
skin. Certain fish are sensitive to electric field changes as small as 10-5
V/m, and some laboratory mammals also respond to significantly weaker fields
than humans. For these electric and acoustic stimuli the reported levels of
geophysical precursors are within the reported perceptible range of some
animals which show unusual behavior prior to earthquakes. In addition, stimuli
caused by the release of gases from small cracks may well be perceived by some
animals before earthquakes. Recent research has confirmed the remarkable
olfactory sensitivity of some animal species, but no quantitative comparisons
with geochemical precursors can be made yet. We find no evidence that magnetic
field precursors or precursory high frequency (above 10 kHz) sounds are the
cause of unusual animal behavior before earthquakes. Although some animals are
highly sensitive to these stimuli, observed magnetic precursors tend to be of
low amplitude amid relatively high noise levels, and high-frequency sound is
severely attenuated within a short distance from the earthquake hypocenter.
Knowledge of animal sensory capabilities may suggest an instrumental strategy
for detecting earthquake precursors. We recommend further geophysical research
in seismic areas to measure (1) seismic waves in the frequency range 10-50 Hz,
(2) earthquake-related electric field changes and air ionization, and (3)
coseismic or preseismic release of trapped gases other than radon. Further
biological research can refine our understanding of (1) responses to sounds
and vibrations with frequencies below 50 Hz, (2) the effects of electrical and
electrostatic changes on animal behavior, (3) behavioral responses to odors,
and (4) sensory capabilities of common domestic animals like horses, dogs, and
chickens, which are seldom studied but commonly mentioned in the preearthquake
reports.