SEGJ Technical Conference

Shallow subsurface structure of Iwate Volcano, northeast Japan, constrained by a helicopter-borne EM and magnetic survey

Abstract A new aeromagnetic anomaly map of Iwate volcano has been published by the Geological Survey of Japan/AIST recently, on the basis of the compilation of aeromagnetic anomalies observed by a helicopter-borne EM and aeromagnetic survey conducted over the volcano in 2000. The observed magnetic data has been processed and total magnetic intensity anomalies and RTP anomalies have been calculated on a smoothed observed surface. Whereas, apparent resistivity maps were created for each sampling frequencies of 220, 1,100, 5,500, 27,500 and 137,500 Hz. In general, the characteristics of the distribution of RTP anomalies and apparent resistivities are similar to each other. RTP and apparent resistivity lows lie on Nishi-Iwate volcano, while RTP and apparent resistivity highs lie on Higashi-Iwate volcano. Coincidences of local lows of RTP anomalies and apparent resistivities often correspond to the geothermal alteration areas confirmed by geologic mapping. It is concluded that the airborne method is useful to map alteration areas in stratovolcanoes with rugged terrain.