Stress drop variations of induced earthquakes at the Basel geothermal site

Goertz‐Allmann, Bettina P.; Goertz, A.; Wiemer, Stefan

doi:10.1029/2011gl047498

Cited by 205 publications

(166 citation statements)

References 29 publications

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“…Isotropic moment tensor components may relate to the occurrence of long-period events (Bame and Fehler, 1986;Ferrazzini et al, 1990;Jousset et al, 2010). The locations of the events with high isotropic components also coincide with previously found regions of high -values (Bachmann et al, 2012) and low stress drops (Goertz-Allmann et al, 2011).…”

Section: Basel Switzerlandsupporting

confidence: 65%

“…However, the multiple injection operations at TR8A can be responsible for changing dominant fluid migration pathways, and indirectly may be responsible for the occurrence of LME in the Berlin geothermal field. They also found a dependence of stress drop on distance from the injection point, somewhat similar to what was found by Goertz-Allmann et al (2011) for Basel, but not nearly as well defined.…”

Section: Source Mechanism Of Larger Magnitude Events (Lme)supporting

confidence: 64%

“…Assuming that earthquakes occurring in regions of high differential stress or on faults with large shear stresses, on average tend to have higher stress drops, one should expect a systematic spatial variability of earthquake stress drops similar to the variability observed for the -values. In fact, the stress drops determined by Goertz-Allmann et al (2011) for the induced seismicity of Basel vary over a wide range and tend to increase systematically with distance from the injection point and, thus, with time. Zhao et al (2014) analysed the 19 largest events that occurred during and after the injection sequence and determined moment tensors from full waveforms.…”

Section: Basel Switzerlandmentioning

confidence: 99%

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Analysis of induced seismicity in geothermal reservoirs – An overview

et al. 2014

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In this overview we report results of analysing induced seismicity in geothermal reservoirs in various tectonic settings within the framework of the European Geothermal Engineering Integrating Mitigation of Induced Seismicity in Reservoirs (GEISER) project. In the reconnaissance phase of a field, the subsurface fault mapping, in situ stress and the seismic network are of primary interest in order to help assess the geothermal resource. The hypocentres of the observed seismic events (seismic cloud) are dependent on the design of the installed network, the used velocity model and the applied location technique. During the stimulation phase, the attention is turned to reservoir hydraulics (e.g., fluid pressure, injection volume) and its relation to larger magnitude seismic events, their source characteristics and occurrence in space and time. A change in isotropic components of the full waveform moment tensor is observed for events close to the injection well (tensile character) as compared to events further away from the injection well (shear character). Tensile events coincide with high Gutenberg-Richter -values and low Brune stress drop values. The stress regime in the reservoir controls the direction of the fracture growth at depth, as indicated by the extent of the seismic cloud detected. Stress magnitudes are important in multiple stimulation of wells, where little or no seismicity is observed until the previous maximum stress level is exceeded (Kaiser Effect). Prior to drilling, obtaining a 3D -wave ( ) and -wave velocity ( ) model down to reservoir depth is recommended. In the stimulation phase, we recommend to monitor and to locate seismicity with high precision (decametre) in real-time and to perform local 4D tomography for velocity ratio ( / ). During exploitation, one should use observed and model induced seismicity to forward estimate seismic hazard so that field operators are in a position to adjust well hydraulics (rate and volume of the fluid injected) when induced events start to occur far away from the boundary of the seismic cloud.

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Section: Basel Switzerlandsupporting

confidence: 65%

Section: Source Mechanism Of Larger Magnitude Events (Lme)supporting

confidence: 64%

Section: Basel Switzerlandmentioning

confidence: 99%

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Analysis of induced seismicity in geothermal reservoirs – An overview

et al. 2014

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“…Goertz- Allmann et al (2011) analyzed stress drops of earthquakes induced by a waterinjection experiment into a borehole and obtained a clear increase in the stress drop as a function of distance from the injection point, thus suggesting that the stress drop correlates with pore pressure perturbations due to the injection. Tomic et al (2009) estimated stress drops of reservoir-induced earthquakes with M ≤ 2.1 and concluded that the values were similar to those of natural earthquakes.…”

Section: Studies On Seismicity and Stress Dropmentioning

confidence: 99%

Migration of earthquakes with a small stress drop in the Tanzawa Mountains, Japan

et al. 2015

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A cluster of earthquake activity took place beneath the Tanzawa Mountains at a depth of 20 km during the end of January 2012. The activity began at 22:39 UT on January 27 and included 78 earthquakes with magnitudes of 2.0 and greater within the span of 50 h. Five of them had magnitudes greater than 4.0, and the largest one was a M5.4 earthquake. We relocated the hypocenters by using the double-difference method and characterized their migrations away from the first earthquake of the cluster activity. The migration was consistent with fluid diffusion and had a similar speed to that of non-volcanic tremors and of induced earthquakes caused by water-injection experiments. We then analyzed stress drops for 16 earthquakes of M3.5 and greater that occurred from July 2003 to June 2012 in the area of the cluster activity. Earthquakes that occurred before and after the cluster activity had typical and stable values of stress drop. This is consistent with structural studies indicating the existence of little fluid in the region. In contrast, the cluster activity included earthquakes with significantly small stress drops. The leading hypothesis is that the cluster activity was associated with a decrease in the shear strength due to an increase in pore pressure, and this can explain both the migration of hypocenters and the small stress drops associated with the cluster activity. This hypothesis is also supported by the fact that earthquakes before and after the cluster activity had similar values of stress drop, thus suggesting that the activity was triggered by a different mechanism from the other earthquakes in the same region. The most plausible explanation is that there is a little fluid in the closed system beneath the Tanzawa Mountains that is undetectable by structural observations.

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“…[78,79]. In the case of forced fluid circulation in a geothermal field, it is also possible that a reduction of differential stress due to pore pressure increase leads to reduced stress drop, as observed by Goertz-Allmann et al [80]. Finally, the self-similarity of earthquakes characteristics, such as stress drop versus seismic moment, is still subject of debate, although several observations for both earthquakes and induced seismic events are consistent with constant stress drops for magnitudes ranging between 9 and -4, e.g.…”

Section: Intact Rock (Red Line) Which In Addition Have Cohesion (C)mentioning

confidence: 59%

Induced seismicity in geothermal reservoirs: A review of forecasting approaches

Gaucher

Schoenball

Heidbach

et al. 2015

Renewable and Sustainable Energy Reviews

159

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In order to reach Europe's 2020 and 2050 targets in terms of greenhouse gas emissions, geothermal resources will have to contribute substantially to meeting carbon-free energy needs. However, public opinion may prevent future large-scale application of deep geothermal power plants, because induced seismicity is often perceived as an unsolicited and uncontrollable side effect of geothermal development. In the last decade, significant advances were made in the development of models to forecast induced seismicity, which are either based on catalogues of induced seismicity, on the underlying physical processes, or on a hybrid philosophy. In this paper, we provide a comprehensive overview of the existing approaches applied to geothermal contexts. This overview will outline the advantages and drawbacks of the different approaches, identify the gaps in our understanding, and describe the needs for geothermal observations. Most of the forecasting approaches focus on the stimulation phase of enhanced geothermal systems which are most prone to generate seismic events. Besides the statistical models suited for realtime applications during reservoir stimulation, the physics-based models have the advantage of considering subsurface characteristics and estimating the impact of fluid circulation on the reservoir. Hence, to mitigate induced seismicity during major hydraulic stimulations, application of hybrid methods in a decision support system seems the best available solution. So far, however, little attention has been paid to geochemical effects on the failure process and to production periods. Quantitative modelling of induced seismicity still is a challenging and complex matter. Appropriate resources remain to be invested for the scientific community to continue its research and development efforts to successfully forecast induced seismicity in geothermal fields. This is a prerequisite for making this renewable energy resource sustainable and accessible worldwide.

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Stress drop variations of induced earthquakes at the Basel geothermal site

Cited by 205 publications

References 29 publications

Analysis of induced seismicity in geothermal reservoirs – An overview

Analysis of induced seismicity in geothermal reservoirs – An overview

Migration of earthquakes with a small stress drop in the Tanzawa Mountains, Japan

Induced seismicity in geothermal reservoirs: A review of forecasting approaches

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