Read this in The Manila Times digital edition.
WE are all seeing what happened in Turkey a week ago — two earthquakes 7.8 and 7.5 magnitude took place within a span of nine hours, affecting areas within a 50 kilometer radius. About 40,000 dead, cities razed to the ground, whether built up with high-rise buildings or smaller edifices. We had a similar if much less horrific experience last year in Abra, with twin earthquakes. The first and the second Abra earthquakes came within days of each other. As explained by Dr. Mario Aurelio, an earthquake scientist now with the National Geological Sciences Institute, earthquakes are generated by a slipping point in the release of stresses between tectonic plates that are pushing each other. The segment that slips causes an earthquake. An earthquake that occurs in an area is said to have experienced stress after and therefore there is not likely to be another earthquake immediately in that area. But stresses that are released do not disappear but transfer to another location. In this other location, the stress increase will, if built up enough, slip in time and cause the next earthquake. The term used to measure rupturing faults is the Coulomb stress transfer (CST), in case you see these initials in reports of earthquakes.
Dr. Aurelio knows whereof he speaks from studies and experience. He was part of the team that studied the Izmit segment of the North Anatolian Fault System after the 7.6 earthquake in 1997 in Turkey (the country now calls itself Turkiye). This is the area within the East Anatolian Fault, a region of active faults which includes the boundary between two tectonic plates — the Arabian Plate and the Anatolian Block. These tectonic plates push each other, a pressure or push termed extrusion tectonics. They, of course, build up stress which will soon have to slip. Anything in between is squeezed like a watermelon between two solid objects pushing against each other. The other quaint term is "watermelon tectonics," a dreaded earthquake event.
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