Article,
Magnetotelluric and geomagnetic modelling reveals zones of very high electrical conductivity in the upper crust of Central Java
Physics of the Earth and Planetary Interiors, 124 (3-4): 131--151 (August 2001)
DOI: 10.1016/S0031-9201(01)00196-0
Abstract
We present results of two- and three-dimensional modelling of magnetotelluric
and geomagnetic data from Central Java, Indonesia. We adopt a hypothesis
testing approach, where we examine the influence of individual structural
elements of competing models on the total model responses. The models
show that ocean anomalies do not overwhelm the signal due to strong
electrical conductivity anomalies within Java. These highly conducting
regions with resistivities of below 1 Ohm m are located in the central
and northern parts of the island. Fitting of the geomagnetic data
requires that the innermost parts of both regions consist of material
with extremely low resistivity (0.2 Ohm m). Young sediments, tephra
and their alteration products can be responsible for some of the
low resistivity regions at shallow depths. The two zones of extremely
high conductivity, however, are best explained as consequences of
geothermal activity in the vicinity of active volcanism (Mt. Merapi)
in Central Java and by fluid or graphite enrichment along shear zones
in northern Java. Subduction zone related processes in a depth range
of 70-400 km cannot be resolved because the highly conductive regions
at shallow depths effectively screen deeper structures.
