Seismic velocity variations accompanying shallow magmatic dyke activity

• Thesis title in Czech: Změny seismických rychlostí během mělké magmatické aktivity
• Thesis title in English: Seismic velocity variations accompanying shallow magmatic dyke activity
• Academic year of topic announcement: 2022/2023
• Thesis type: dissertation
• Thesis language: angličtina
• Department: Institute of Hydrogeology, Engineering Geology and Applied Geophysics (31-450)
• Supervisor: prof. RNDr. Tomáš Fischer, Ph.D.
• Author: hidden - assigned by the advisor
• Date of registration: 10.10.2022
• Date of assignment: 10.10.2022

Preliminary scope of work

viz anglická verze

Preliminary scope of work in English

Earthquake swarms are typified by migration of hypocenters, which is usually attributed to the propagation of crustal fluids and/or magma dyke. This implies a liquid phase is present in the focal volume of the earthquake swarms, which could be detected by the anomalies of seismic velocities and the Vp/Vs ratio.
Various methods were recently proposed to analyze the space and time seismic velocity variations in detail. One of them is the Wadati-DD method which allows for mapping the velocity ratios in the focal volume of earthquake swarms or aftershocks (Lin and Shearer, 2007; Dahm and Fischer, 2014; Bachura and Fischer, 2016). Another is the interferometric methods. Among them the intersource interferometry (Eulenfeld, 2020) appears promising for studying the variation of seismic velocities between earthquake clusters. Both these methods were successfully applied to seismic swarms in West Bohemia and showed velocity anomalies in the focal volume. The possible origin of observed anomalies in fluid accumulations however could not be proved as independent observations of fluids in the fault zone are missing.
A new light to this problem could be brought by analyzing the Reykjanes Fagradalfjall 2021 and 2022 seismic swarms that were followed by the eruption right on the top of the swarm seismicity. This suggests that the seismicity was driven by magma propagation. In this PhD project different methods of seismic velocity analysis will be combined to verify their ability of identifying a magma dyke in the shallow crust.

References
Bachura M., Fischer T., 2016. Detailed velocity ratio mapping during the aftershock sequence as a tool to monitor the fluid activity within the fault plane. Earth Planet. Sci. Lett., 453, 215-222., doi: 10.1016/j.epsl.2016.08.017
Dahm, T., and Fischer, T., 2014. Velocity ratio variations in the source region of earthquake swarms in NW Bohemia obtained from arrival time double-differences. Geophys. J. Int. 196, 957–970, doi: 10.1093/gji/ggt410.
Eulenfeld, T. (2021). Toward source region tomography with intersource interferometry: Shear wave velocity from 2018 West Bohemia swarm earthquakes. Journal of Geophysical Research: Solid Earth, 125, e2020JB019931. https://doi.org/ 10.1029/2020JB019931
Lin, G., Shearer, P., 2007. Estimation local Vp /Vs ratios within similar earthquake clusters. Bull. Seismol. Soc. Am. 97, 379–388. http://dx.doi.org/10.1029/ 2009GL039098.