Geomagnetic diurnal-variation anomalies and their relation to strong earthquakes

Introduction The occurrence of earthquake has relations not only with seismogenic process of source area,but also with the environment of inner (earth space) and outer (earth-sun space). The varyinggeomagnetic field is natural medium that connects with both factors (DING, 1988). There are two kinds of basic ideas using the diurnal-variation anomalies of the verti-cal-component (Z) in geomagnetic field to predict earthquake. The first kind is local geomagneticanomalies that are obta…

Geomagnetic diurnal-variation anomalies and their relation to strong earthquakes

The diurnal-variation anomalies of the vertical-component in geomagnetic field are mainly the changes of phaseand amplitude before strong earthquakes. On the basis of data recorded by the network of geomagnetic observatories in China for many years, the anomalous features of appearance time of the minima of diurnal variations (i.e,low-point time) of the geomagnetic vertical components and the variation of their spatial distribution (i.e, phenomena of low-point displacement) have been studied before over 30 strong earthquakes with Ms≥6.6 such asKunlunshan Ms=8.1 earthquake on November 14, 2001; Bachu-Jashi Ms=6.8 earthquake on February 24, 2003;Xiaojin Ms=6.6 earthquake on September 22, 1989, etc. There are good relations between such rare phenomena ofgeomagnetic anomalies and the occurrence of earthquakes. It has been found that most earthquakes occur in thevicinity of the boundary line of sudden change of the low-point displacement and generally within four days beforeand after the 27th or 41st day counting from the day of appearance of the anomaly. In addition, the anomalies ofdiurnal-variation amplitude near the epicentral area have been also studied before Kunlunshan Ms=8.1 earthquakeand Bachu-Jiashi Ms=6.8 earthquake.