V13C-3154
Seismic Study of the Velocity Structure and Earthquake FocalMechanisms beneath the Krafla Central Volcano, NE Iceland
Monday, 14 December 2015
Poster Hall (Moscone South)
Juerg Schuler1, Tim S Greenfield2, Robert S White2, Steven W Roecker3, Bryndis Brandsdottir4, Joann M Stock5, Jon Tarasewicz6, Hilary Rose Martens1 and David J Pugh7, (1)California Institute of Technology, Pasadena, CA, United States, (2)Bullard Laboratories, Cambridge, United Kingdom, (3)Rensselaer Polytechnic Inst, Troy, NY, United States, (4)University of Iceland, Reykjavik, Iceland, (5)California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States, (6)BP, Sunbury on Thames, United Kingdom, (7)University of Cambridge, Cambridge, CB3, United Kingdom
Abstract:
We investigated the seismic velocity structure of the Krafla central volcano, NE Iceland, and its shallow geothermal fields. In our 3D tomographic inversions, we used passive seismic data recorded between 2009-2012 from a temporary local network as well as active seismic legacy data to constrain the velocity models. We find high P-wave velocities (Vp) underneath regions of elevated topographic relief as well as two low-Vp anomalies that coincide spatially with two attenuating bodies outlined from S-wave shadows during the Krafla rifting episode of 1974-1985. Within the Krafla geothermal reservoir, which is developed for energy production, we imaged a shallow low-Vp/Vs zone overlying a deeper high-Vp/Vs zone and interpreted them as steam- and brine-bearing formations, respectively. Previously undertaken borehole measurements support our findings. A prominent low-Vp/Vs anomaly underlies these zones at rock depths greater than 1.5 km, where a super-heated zone within felsic overlies rhyolitic within the geothermal melt. Calculations systems show that of the most earthquake focal events are mechanisms consistent double-couple source models with only a few clear non-shear source models.
