Geomagnetic total intensity variations associated with vertical crustal movements in the eastern part of the Izu Peninsula
Masahiro SASAOKA, Takeshi OWADA, Shin ARITA, Akira YAMAZAKI, Yosuke TAGUCHI and Tsutomu OGAWA
Abstract
Earthquake swarms and anomalous crustal activities took place in the eastern part of the Izu Peninsula from 2010 to 2012; to detect the geomagnetic changes associated with these disturbances, we continuously measured geomagnetic total intensity and removed the effects of external magnetic fields. The daily variations in the geomagnetic field were associated with daily variations in the vertical crustal movements revealed by the geodetic height measured by GPS (Global Positioning System). Although we observed no significant seasonality in geomagnetic total intensity during the quiet seismic period of 2012, daily variations of vertical crustal movements changed seasonally during 2010-2012, as did the daily variations of the geomagnetic total intensity during both the quiet seismic period of 2010 and during the relatively active seismic period of 2011. We infer that hydrothermal activity related to the December 2009 earthquake swarm (caused by magma injection) persisted for less than two years and that hydrothermal movements associated with vertical crustal movements caused the seasonal changes in geomagnetic total intensity during 2010-2011. The implication is that the observed variations of the geomagnetic total intensity were not directly associated with seismic faulting. Continuous observations of geomagnetic total intensity are expected to facilitate prediction of the course of earthquake swarm activity in the eastern part of the Izu Peninsula.
(Received 30 October 2013; received in revised from 28 February 2014; accepted 3 march 2014)
