Abstract
AbstractWe examine the relationship between earthquakes and ultralow frequency (ULF) wave activity in the nighttime ionosphere based on the electric field data in the direct current/ULF range observed by the DEMETER satellite over a ~5.5 year period from May 2005 to November 2010. ULF wave activity is identified by an automatic detection algorithm and those which occur on the geomagnetic disturbed days (Kp > 3 at any time intervals) are discarded. Only the earthquakes with depth ≤70 km and occurring in the region of |MLat| < 40° are selected. A superposed epoch analysis is performed to study the statistical association between ULF wave activity and the selected earthquakes. The results show that (1) there are clearly temporal and spatial correlations between ULF wave activity and earthquakes whose catalog magnitudes are both ≥4.8 and ≥5.0, and (2) enhanced ULF wave occurrence rate happens ~1 day and 1 week before the earthquakes and at less than 200 km distance from the epicenters.
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