First results of a multiphysics experiment at Krafla geothermal volcano: Seismicity pattern from joint hypocenter-3D travel-time tomography inversion

The IMPROVE ITN project focuses its interdisciplinary approach on a better understanding of volcanic systems, partly with multiphysics imaging methods. One target of this project is Krafla, a volcano of the northern volcanic zone in Iceland, which erupted last during the Krafla fires in the 1970s and 80s. Also, in this period the national power company of Iceland (Landsvirkjun) built a geothermal powerplant inside the Krafla caldera, increasing the knowledge of the complex system through electro-magnetic and seismic imaging methods and seismological observations.
Nonetheless, the high-resolution imaging of the magmatic system still poses a challenge just as the origins of the seismicity remain poorly understood. To tackle these questions a multi-physics experiment has been carried out in June and July 2022.
The experiment included an active 3D ERT experiment to image the first kilometre of the geothermal system, the densification of the already existing MT measurements and the installation of a dense seismic array of 100 stations deployed for 1 month. In addition, Landsvirkjun provided continuous seismic data acquired from 12 broadband 3-C stations over the last 8 years.
With this dataset we aim to better understand temporal and spatial changes in stress, the anthropogenic influence on the system through the geothermal industrial activity and to image shallow magmatic pockets.
The broadband data of the 12 permanent seismic stations were used to analyse the seismicity with STA/LTA and Template Matching methods. The first P- and S-wave onsets were automatically picked and inverted using a joint hypocentre-velocity approach based on ray theory. It provides a new 3D P-wave velocity model and refined locations of the seismicity.
This updated earthquake catalogue, consisting of seismicity of the last 8 years, covers a deflation and an inflation period of Krafla, yielding the opportunity to better investigate the seismic properties in relation with geothermal industrial activity and long-term deformation of the volcano. The variability of the P-wave velocity will be compared to the available 3D resistivity models obtained from previous MT measurements.
In the future, the dense seismic array will be used for high resolution imaging at the geothermal upflow-systems and jointly interpreted with the ERT and MT data, while the 12 broadband recordings will be used for seismic noise monitoring purposes.