Microearthquake hypocenters were analysed in the Krýsuvík geothermal area in SW-Iceland with data taken from two consecutive passive seismic surveys, 2005 and 2009. Five years prior to the 2005 survey, this area was struck by an earthquake initiating a major top-to-bottom fluid migration in the upper crust. We observe from our surveys a complex bottom-to-top migration of seismicity with time following this fluid penetration, suggesting the migration of a pore pressure front controlled by the upper-crust fracture system. We interpret these data as the time and space development of high-temperature hydrothermal cells from a deep upper crustal fluid reservoir in the supercritical field. These results provide an insight into the coupling mechanisms between active tectonics and fluid flow in upper-crustal extensional systems with high thermal flux.

2005 Data File

See: Geoffroy and Dorbath, GRL, 2008, doi: 10.1029/2008GL034514

2009 Data File

P and S-arrival times of 6,100 events were detected by at least 10 stations. First, the earthquakes were located using the local 1D Vp model. Second, arrival times for the 2830 best-located events, including differential arrival times measured by cross correlation, were inverted using TomoDD, which solves simultaneously absolute hypocenter locations with relative constraints and 3D P- and S-waves velocity structure. To increase the robustness of the velocity model as well as earthquake relocation, and to reduce dependency on the initial model velocity and the grid parametrization, we applied the post-processing WAM (Weighted Average Model) method. This method consists of calculating a semblance-weighted average of many velocity models inverted with various geometries of the input velocity grid. It allows estimating the reliability of the velocity anomalies based on the standard deviation of the velocity values at each node of the fixed grid. The final uncertainty of hypocenter locations was estimated less than 140 m in the three directions.

1) Those data are currently exploited in on-going research ending January, 1 2024.

2) See README file for the use of the dataset