Satgen584 Satellite Seismology  by GM4IHJ  (BID SGEN584)  2000-06-03

In June 92, Southern California was shaken by an earthquake. By good
fortune the epicentre was out in open desert country near Landers. So
no great urban damage resulted, and by coincidence the European ERS-1
satellite had just previously, taken a side scan synthetic aperture
radar picture of the Landers area. So immediately after the quake
more ERS-1 pictures of the area were obtained. Pictures before and
after were then compared and it was possible to see how far each 4 x
20 metre pixel of ground had been moved by the quake. Since then
ERS-1 has gone on to record ground displacement features on swelling
volcanoes prior to their eruption . It has watched as volcanoes under
an ice cap caused minor changes at the immediate point above the cone
, but sent torrents of hot melt water roaring out from under the edge
of the ice cap , washing away bridges and roads and everything else
in their path . While in warmer climes it has monitored the potential
for mud slides on tropical volcanoes,when heavy rain sends mud slides
to engulf villages far from the erupting volcanic cone.

Regular sequences of pictures taken by ERS-1 and its 1995 successor
ERS-2. Have given data on the effects of ionospheric and tropospheric
disturbance on the signals, as well as revealing the effects of deep
snow falls on sites of interest , plus the far less than expected
effects of thick tropical vegetation , on signal reflections from the
ground.

So it is no surprise that American scientists are pressing for their
own SAR satellite. Which will be called InSAR and will hopefully be
funded through NASA. Noting that, while ERS-2 works well, it does not
provide regular images of the USA, in a time scale commensurate with
American requirements. Given that USA ( along with Turkey, Indonesia
and Japan, amongst others), has more areas of immediate seismic
concern than anywhere else in the world. For while the rest of the
world has one or two of the super caldera type , world wide disaster
provoking locations. Western USA alone has Yellowstone, Long Valley,
Valle Grande and several other sites , all capable of matching or
surpassing the destructive power of past events. Such as that which
occured around 538 AD . When Krakatoa in Sunda Strait, exploded and
caused a nuclear winter all over the earth. Resulting in the deaths
of millions of people in the subsequent icy cold and famine caused by
a dust cloud which blocked out the Sun for months, and which has been
blamed by some historians, for the collapse of civilizations as far
apart as Teotihuacan, and the Easter Roman Empire.

Aside from volcano watching . Large conurbations in the Western USA
located on or near well known earthquake fault lines, need a constant
earth watch , and while InSAR cannot, as far as we know presently,
provide prior warning of earthquakes. It can be expected to usefully
supplement, the already partially funded Earth Scope terrestrial
surface and drilling experiment, planned for that part of the USA.
Whilst the already available ground monitoring system provided by
the repeated measurement at selected locations, of Global positioning
location and altitude data, is also useful, albeit rather more labour
intensive.