Geoscience Reference
In-Depth Information
these faults. The first stage of a successful short-time prediction would be a suc-
cessful detection of active faults. However, the identification of an earthquake
producing fault is not easy. In Japan, it took 14 years to survey 110 active faults
but the next 6 major earthquakes (6.9-7.3) occurred along undetected ones. They
suggested that the location and geometry of a source fault of a future earthquake
can be inferred from fold structure. Other methods to get information about hidden
faults are seismography and Radar imaging. Seismic data are used to detect faults
with no ruptures on the earth's surface. Talebian et al. examined the 2005 Dah-
uiyeh earthquake sources (Talebian et al.
2006
). They used seismic body waves,
radar interferometry and field investigation to examine the source processes of the
destructive earthquake. Using Landsat TM, ETM and SAR ERS-1 data and con-
ducting long term monitoring of tectonic structures they identify linear features
(active faults). Currently, researchers concentrate their efforts on identifying local
and hidden faults and monitoring the precursory events along them. Infrared
images are used to show thermal anomalies around fault zone for past earthquakes.
Higher concentration of atmospheric water vapor along nearby active faults was
reported 11 days before Wenchuan earthquake (Liu et al.
2007
).
Scientists used Landsat TM, ETM and SAR ERS-1 data to successfully detect
linear features on the earth's surface (faults) through visual interpretation (Zoran
2010
). They reported that remote sensing multi-spectral images have great
potentials in large scale active faults investigation. They declared fabulous result
of their efforts in detection of invisible faults. They attributed the successfulness of
remote sensing to its wide recording spectrum from visible to microwave. Nev-
ertheless, those faults buried by soil layers may not be detected with satellite-based
data.
Proper approach to identify the faults with no ruptures on the earth's surface or
those which have been covered by soil is to perform geochemical surveys. In this
method, sampling is carried away to record the amount of Radon gas in organized
sampling networks or deep into the surface in certain points. By statistical analyses
and re-sampling methods it will be possible to compare the resultant maps with
fault maps and detect invisible faults deep enough to be a path to Radon reach the
earth's surface.
3.2 Heat and Thermal Anomalies
The accumulated stress in the ground causes the generation of two phenomena;
Heat and seismic waves. Heat is a direct result of the compression in underground
rocks. Rocks are packed together to absorb some of the stress. In this level the
underground water comes up causing higher resistance capability of the crustal and
upper crustal part of the ground (Plastino et al.
2010
). But, when the tolerance limit
has passed the rocks break and micro-cracks form. This allows the water to come
back filling the newly formed holes causing the loss of resistance of the whole
system. It is when the ground is waiting for another pressure to rupture or move
