Sensitivity of stress inversion of focal mechanisms to pore pressure changes

Martínez‐Garzón, Patricia; Vavryčuk, Václav; Kwiatek, Grzegorz; Bohnhoff, Marco

doi:10.1002/2016gl070145

Cited by 39 publications

(33 citation statements)

References 37 publications

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“…At the selected location at The Geysers geothermal field, local stresses were found to change, mainly related to fluid injection, which directly affects thermal stresses and pore fluid pressure in the reservoir. On a longer time scale, the stress ratio R was observed to slightly decrease [ Kwiatek et al ., ; Martínez‐Garzón et al ., ]. Within shorter time periods, Martínez‐Garzón et al .…”

Section: Discussionmentioning

confidence: 99%

“…Previously, a number of short‐ and long‐term transients in seismomechanical characteristics were identified that are related to changing injection rates. These include distance of seismicity from injection well, different faulting styles, b values from Gutenberg‐Richter distributions, and stress ratio R from stress tensor inversion [ Martínez‐Garzón et al ., ; Kwiatek et al ., ; Martínez‐Garzón et al ., ]. Importantly, the seismicity from this cluster has revealed significant changes of the stress field orientation of approximately ≈ 15–20° during periods of high injection rates [ Martínez‐Garzón et al ., ].…”

Section: Site Characteristics Seismicity Data and Hydraulic Parametersmentioning

confidence: 99%

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Impact of fluid injection on fracture reactivation at The Geysers geothermal field

et al. 2016

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We analyze the spatiotemporal distribution of fault geometries from seismicity induced by fluid injection at The Geysers geothermal field. The consistency of these faults with the local stress field is investigated using (1) the fault instability coefficient I comparing the orientation of a fault with the optimal orientation for failure in the assumed stress field and (2) the misfit angle β between slip vectors observed from focal mechanisms and predicted from stress tensor. A statistical approach is applied to calculate the most likely fault instabilities considering the uncertainties from focal mechanisms and stress inversion. We find that faults activated by fluid injection may display a broad range in orientations. About 72% of the analyzed seismicity occurs on faults with favorable orientation for failure with respect to the stress field. However, a number of events are observed either to occur on severely misoriented faults or to slip in a different orientation than predicted from stress field. These events mostly occur during periods of high injection rates and are located in proximity to the injection wells. From the stress inversion, the friction coefficient providing the largest overall instability is μ = 0.5. About 91% of the events are activated with an estimated excess pore pressure <10 MPa, in agreement with previous models considering the combined effect of thermal and poroelastic stress changes from fluid injection. Furthermore, high seismic activity and largest magnitudes occur on favorably oriented faults with large instability coefficients and low slip misfit angles.

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Section: Discussionmentioning

confidence: 99%

Section: Site Characteristics Seismicity Data and Hydraulic Parametersmentioning

confidence: 99%

Impact of fluid injection on fracture reactivation at The Geysers geothermal field

et al. 2016

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“…The crustal region beneath the Higher Himalaya shows a nearly N‐S oriented σ 1 with a plunge of 33° and near horizontally plunging E‐W oriented σ 3 with an acceptable misfit angle of 45° (Figure b). The above segments indicate a transpressive stress regime, as our stress inversion results show a relative vertical orientation of σ 2 with respect to σ 1 and σ 3 and a lesser R value (<0.25; e.g., Martínez‐Garzón et al, ). The upper mantle region beneath the Higher Himalaya shows a NNW‐SSE oriented σ 1 with a plunge of 36° and near horizontally plunging ENE‐WSW oriented σ 3 (Figure c).…”

Section: Resultsmentioning

confidence: 64%

“…with an acceptable misfit angle of 45 •(Figure 6b). The above segments indicate a transpressive stress regime, as our stress inversion results show a relative vertical orientation of 2 with respect to 1 and 3 and a lesser R value (<0.25; e.g.,Martínez-Garzón et al, 2016b). The upper mantle region beneath the Higher Himalaya shows a NNW-SSE oriented 1 with a plunge of 36 • and near horizontally plunging ENE-WSW…”

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Rupture of the Indian Slab in the 2011 Mw 6.9 Sikkim Himalaya Earthquake and Its Tectonic Implications

et al. 2019

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Unlike the other Himalayan plate boundary segments, the eastern Nepal to Bhutan Himalayan region is not known to have generated prominent shallow thrust faulting earthquakes, typical of the ongoing convergence. This region features strike‐slip earthquakes over the depth ranges of 40–120 km, indicating intraslab deformation. Here we present for the first time a slip distribution model for the largest recorded intraslab strike‐slip earthquake in this region, the Mw 6.9 Sikkim event that occurred on 18 September 2011. Relying on kinematic source process modeling, our results indicate a NE‐SW trending, steeply dipping sinistral source zone within the underthrusting Indian slab. The rupture propagated radially, with a low rupture velocity of 1.7 km/s, breaking a large asperity of 20 × 20 km2 with a maximum slip of 1.6 m. The rupture nucleated at a depth of 45 km and reached upper mantle depths. The computed coseismic stress drop value is 13.6 MPa. We suggest that most of the aftershocks occurred on the conjugate plane, possibly due to stress triggering. Stress inversion of focal mechanisms indicates a transpressive stress regime throughout the crust and pure strike‐slip regime in the upper mantle. We observed a unimodal distribution of earthquakes beneath the Higher Himalaya. This indicates a strong, brittle Indian slab and unravels a scenario of an eventual breakup of the lithosphere; the key trigger might be variation in the convergence rates along the Himalayan arc.

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“…In order to analyze tectonic stress in the focal zone we use the public‐open Matlab code STRESSINVERSE (http://www.ig.cas.cz/stress-inverse) for a joint inversion of focal mechanisms for stress and fault orientations developed by Vavryčuk (). The method is based on the Michael's inversion for stress (Michael, , ) that is run in iterations and utilizes the fault instability criterion (Martínez‐Garzón et al, ; Vavryčuk et al, ) for discriminating which of two nodal planes is the fault plane. The method is fast and robust and provides uncertainty limits of results.…”

Section: Tectonic Stressmentioning

confidence: 99%

Detection of Stress Anomaly Produced by Interaction of Compressive Fault Steps in the West Bohemia Swarm Region, Czech Republic

Vavryčuk

Adamová

2018

Tectonics

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Observations of the 2008–2014 seismic activity in West Bohemia, Czech Republic, provide evidence of interaction of compressive fault steps that created local stress anomaly and triggered a seismic sequence with exceptional properties. The West Bohemia is a geothermal area, characterized by persistent fluid‐driven seismicity in the form of earthquake swarms. The focal zone is formed by two weak and fluid‐eroded parallel strike‐slip faults with a step of about 200 m. The fault segments were activated successively by the 2008 and 2011 swarms with magnitudes of the strongest events of 3.8 and 3.7, respectively. In 2014, a fracture linking both segments was formed or activated by a mainshock‐aftershock sequence. The aftershock decay was very fast, and the focal mechanism of the strongest event with magnitude of 4.2 was inconsistent with the regional background stress. The stress inversion of 957 focal mechanisms revealed a stress anomaly characterized by interchanging the σ2 and σ3 principal stress axes in the area of fault interaction. The modeling of the Coulomb stress change confirmed that the stress anomaly could completely disturb the regional background stress and produce the rotation of the principal stress axes retrieved from focal mechanisms. The faults activated or newly formed within the compressive stress anomaly were of high strength, which caused the anomalous mainshock‐aftershock character of the 2014 activity and the rapid aftershock decay. Linking the two previously active isolated faults during the 2014 activity increased the expected moment magnitude Mw of a possible strongest earthquake from 5.0 to 5.4.

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Sensitivity of stress inversion of focal mechanisms to pore pressure changes

Cited by 39 publications

References 37 publications

Impact of fluid injection on fracture reactivation at The Geysers geothermal field

Impact of fluid injection on fracture reactivation at The Geysers geothermal field

Rupture of the Indian Slab in the 2011 Mw 6.9 Sikkim Himalaya Earthquake and Its Tectonic Implications

Detection of Stress Anomaly Produced by Interaction of Compressive Fault Steps in the West Bohemia Swarm Region, Czech Republic

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