Article,
Hengill geothermal volcanic complex (Iceland) characterized by integrated geophysical observations
Geothermics, 40 (1): 1--24 (Mar 2, 2011)
DOI: 10.1016/j.geothermics.2010.12.008
Abstract
Structural features of volcanic and hydrothermal systems can be used
to infer the location of magma chambers or productive geothermal
areas. The Hengill volcanic triple-junction complex has a well-developed
geothermal system, which is being exploited to extract hot fluids
that are used for electrical power and heat production. In the framework
of the I-GET project, a 4-month temporary seismological network including
seven high-dynamic broadband instruments was deployed and 1D transient
electromagnetic soundings (TEM) and 3D magnetotelluric (MT) surveys
were performed to improve the understanding of the relationships
between structural features, seismic activity and fluid production
at the Hengill geothermal system. The MT and TEM data set are analysed
elsewhere. The analysis of the seismological data set allowed the
detection and classification of more than 600 earthquakes, among
which long-period (LP) earthquakes were observed for the first time
in this area. This work focuses first on a joint inversion for the
3D velocity structure and determination of the locations of the hypocentres
from about 250 local volcano-tectonic earthquakes with clear P- and
S-wave arrival times. The results confirm those from earlier tomography
studies in this area. Integrating the seismic velocity and resistivity
models in a semi-quantitative approach by cross-plotting the resistivity
model with the velocity ratio VP/VS delineates a structural body
with a high seismic velocity ratio and low resistivity that is interpreted
as the main heat source of the geothermal system.
