08 Jun 2022
08 Jun 2022
Status: this preprint is open for discussion.

Constraints on Fracture Distribution in the Los Humeros Geothermal Field From Beamforming of Ambient Seismic Noise

Heather Kennedy, Katrin Löer, and Amy Gilligan Heather Kennedy et al.
  • School of Geosciences, University of Aberdeen, Aberdeen, AB24 3FX, Scotland

Abstract. Faults and fractures are crucial parameters for geothermal systems as they provide secondary permeability allowing fluids to circulate and heat up in the subsurface. In this study, we use an ambient seismic noise technique referred to as three-component (3C) beamforming to detect and characterise faults and fractures at a geothermal field in Mexico.

We perform 3C beamforming on ambient noise data collected at the Los Humeros Geothermal Field (LHGF) in Mexico. The LHGF is situated in a complicated geological area, being part of a volcanic complex with an active tectonic fault system. Although the LHGF has been exploited for geothermal resources for over three decades, the field has yet to be explored at depths greater than 3 km. Consequently, it is currently unknown how deep faults and fractures permeate and the LHGF has yet to be exploited to its full capacity.

3C beamforming extracts the polarizations, azimuths, and phase velocities of coherent waves as a function of frequency, providing a detailed characterisation of the seismic wavefield. In this study, 3C beamforming of ambient seismic noise is used to determine surface wave velocities as a function of depth and propagation direction. Anisotropic velocities are assumed to relate to the presence of faults giving an indication of the maximum depth of permeability, a vital parameter for fluid circulation and heat flow throughout a geothermal field.

3C beamforming was used to determine if the complex surface fracture system permeates deeper than is currently known. Our results show that anisotropy of seismic velocities does not decline significantly with depth, suggesting that faults and fractures, and hence permeability, persist below 3 km. Moreover, estimates of fast and slow directions, with respect to surface wave velocities, are used to determine the orientation of faults with depth. The North-East (NE) and North-North-West (NNW) orientation of the fast direction corresponds to the orientation of the Arroyo Grande and Maxtaloya-Los Humeros fault swarms respectively. NE and NNW orientations of anisotropy align with other major faults within the LHGF at depths permeating to 6 km.

Heather Kennedy et al.

Status: open (until 20 Jul 2022)

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Heather Kennedy et al.

Heather Kennedy et al.


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Short summary
The energy transition is an important topic for benefiting the future, thus renewable energy is required to reach net-zero carbon emission goals. Geothermal energy, heat from the ground, can be used in this transition. Therefore, geothermal fields need to be characterised as much as possible to allow for increased productivity within these fields. This study involves, and looks at potential fractures within a geothermal field at depth to help increase the overall understanding of this field.