SEMINAR: RE: MGG Student Seminar Tuesday April 9

[Monica Arienzo <marienzo@rsmas.miami.edu>]

MGG Student Seminar
Tuesday April 9 - 12:00pm - CIMAS Conference Room

Qiong Zhang


Three-diemsinal seismic tomographY in Coso GEOTHERMAL FIELD: where is the heat source?


Abstract:
The Coso Geothermal Field is located at the west edge of the Basin and Range province and within the Eastern California Shearer Zone. Fumaroles are present along faults bounding the rhyolite-capped horst and locally within the rhyolite field. Due to the presence of the youth rhyolite lavas, hot springs and fumaroles, a magma body was proposed to be the source of thermal energy for the geothermal system. There is a discrepancy in identifying where the magma body exists among diverse geophysical and geological analyses. We apply the seismic tomography and earthquake relocation techniques to map the Vp, Vp/Vs variations underneath the geothermal field. The most striking feature of the resulting velocity model is that the low Vp, low Vs, low Vp/Vs anomaly exists between 6 and 12 km underneath the Coso Hot Springs accompanied by the ductile behavior shown by lack of seismicity. This could be interpreted to be the magma body in the vicinity of high temperature hot water system. The low Vp, low Vs, high Vp/Vs anomaly is observed from the surface to 3 km depth beneath the Sugarloaf Mountain, the largest rhyolite domes in Coso, which we interpret as the intrusive dike. The velocities in the top layers of our model are correlated with the surface geological features. The fault zones and basin areas, such as the Little Lake fault zone, the Airport Lake fault zone and the Indian Wells Valley show low-velocity anomalies. Our high-resolution velocity model images the detailed velocity structure beneath Coso and supports the existence of magma body in crust.


&

Putri Akmal


Determination of the Permeability of South Chamorro Seamount in Mariana Forearc Crust
using Pressure Response to Tidal Loading Method

Abstract:
Pore pressure variations, as the response to transient loading from ocean tides imposed at the seafloor, have been observed by in-situ borehole observatory ODP 1200C located in Mariana forearc region. These pore pressure variations depend on the elastic and hydraulic (transport) properties of the formation.

In this study, we used the analytic solution and model derived by Wang and Davis (1996) in analyzing the amplitude and phase of these formation pressure response relative to seafloor pressure response  in order to deduce constraints on these formation properties,  particularly frame bulk modulus and permeability. Permeability controls the patterns and rates of the fluid flow in oceanic crust that is  important in transferring heat from cooling lithosphere, in carrying solutes to the seafloor and in altering the composition and  physical properties of the crust [Davis et al.,2000].

The resultant permeability values is 2 x 10-13 m2 over the formation-scale of 176 meter from borehole. This result has a little higher order of magnitude with the permeability estimated by Wheat et al (2008) using radial diffusion equation. The advantage of using tidal loading method is that we can estimate the permeability over the larger scale (formation scale) when compared to other methods for estimating the permeability, such as laboratory measurement using core samples where the cracks and fractures are usually not represented in.

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