Tectonic stress regime in the 2003–2004 and 2012–2015 earthquake swarms in the Ubaye Valley, French Alps

Fojtíková, Lucia; Vavryčuk, Václav

doi:10.1007/s00024-018-1792-2

Cited by 19 publications

(13 citation statements)

References 44 publications

(85 reference statements)

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“…As shown by Leclère et al () for the 2004–2005 crisis, such heterogeneous structures, and therefore mechanisms, are not compatible with a unique, static, stress state. Fojtíková and Vavryčuk () also found that a very low friction coefficient of 0.2–0.3 is required. Therefore, either high fluid‐pressure or heterogeneous stress state are required to induce slips on badly oriented structures.…”

Section: Discussionmentioning

confidence: 99%

“…The seismic clusters outside the main structure occurred on structures with various azimuths. By inverting focal mechanisms for the 2003–2004 crisis (Leclère et al, ) and the 2012–2015 crisis (Fojtíková & Vavryčuk, ), the stress field shows a subhorizontal minor component σ3 oriented ~N100° and a N11 to 29° σ1 component, with a plunge between 12° and 61° depending on the authors. Such stress field is compatible with slip on N160° structures, such as the deep ones.…”

Section: Discussionmentioning

confidence: 99%

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Fluid‐Induced Swarms and Coseismic Stress Transfer: A Dual Process Highlighted in the Aftershock Sequence of the 7 April 2014 Earthquake (Ml 4.8, Ubaye, France)

et al. 2019

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The upper part of the Ubaye Valley (French Alps) is characterized by alternating mainshock-aftershock sequences and swarms. Particularly, during the 2012-2015 crisis, four mainshocks with Ml > 3.5 occurred. We here focus on the aftershocks of the largest one (Ml = 4.8, 7 April 2014), in order to better understand the involved processes behind this peculiar seismic behavior. We use template matching detection, waveform classification, and double-difference relocations to analyze this seismicity, on average and at the scale of the clusters that compose it. Most event sources are aligned along a plane consistent with the mainshock fault (N165, 65°W), but occurred on conjugate structures. A few clusters of seismicity are also observed far from the mainshock source. Our analysis shows that distinct, spatially separated processes are at play. While coseismic stress transfer explains the seismicity close to the mainshock source, fluid-pressure diffusion and distant stress triggering are required to generate events farther away. The overall distributions in time and magnitude followed a slow Omori's decay and a Gutenberg-Richter relationship, respectively. However, these classical responses arise from the superposition of very different behaviors, associated with different processes at depth.Plain Language Summary Earthquakes have regularly shaken the upper part of the Ubaye valley, near the town of Barcelonnette in the Southwestern French Alps, for nearly 20 years. The earthquake behavior is peculiar, as swarms of numerous low magnitude events alternate with larger earthquakes, such as the Ml 4.8 one occurring on 7 April 2014. To understand this dual behavior, we performed an in-depth analysis of the aftershock of this event. The seismicity mainly aligns on a plane consistent with the mainshock fault (N165, 65°W). However, most of the events occurred on branching structures, belonging to the damaged zone of this fault, or on some other small faults far away. While the average behavior of this aftershock sequence is close to a standard one, we show that two different processes occurred at depth. Events occurring close to the mainshock are triggered by coseismic stress transfer, while fluid-pressure diffusion are likely required to explain the seismicity further away. Such dual process should be considered for seismic hazard assessment.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Fluid‐Induced Swarms and Coseismic Stress Transfer: A Dual Process Highlighted in the Aftershock Sequence of the 7 April 2014 Earthquake (Ml 4.8, Ubaye, France)

et al. 2019

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“…Mathey et al (2021b) found that the extensional component is oblique to the strike of the Alpine belt, while it was assumed normal until now (Sue et al 2007). Similar stress-states have been reconstructed for the last swarms (2003-2004 and 2012-2015) occurring in the Ubaye Region (Leclère et al 2013;Fojtíková and Vavryčuk, 2018). Focal mechanisms of the largest events are from several catalogues: Fréchet and Pavoni (1979), Leclère et al (2013), Thouvenot et al (2016), FMHex20 (Mazzotti et al 2021) and Mathey et al (2021a).…”

Section: Tectonic Contextmentioning

confidence: 62%

Swarms and mainshock–aftershocks sequences are both triggered by fluids in the Ubaye Region (Western Alps)

Baques

Barros

Godano

et al. 2023

Geophysical Journal International

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Summary The Ubaye Region (French Western Alps) is one of the most seismically active regions in France. It is regularly struck by mainshock-aftershocks sequences like in 1959 (ML5.3), seismic swarms (2003–2004), and complex sequences (2012–2015) characterized by successive mainshocks clustered in time and space. This diversity of seismic behaviour highlights the complex processes at play in this area. To improve our understanding of these processes, in this study, we compile a regional catalogue of existing focal mechanisms, completed by 100 new calculated focal mechanisms of aftershocks following the 07/04/2014 mainshock (ML5.1). The oriented stress-state we reconstruct for different periods and sub-areas are similar to each other and to previous published values focusing on swarm periods. We then calculate fluid-pressure required to trigger the earthquakes. Most of the events (65 per cent) need fluid-overpressure between 15 and 40 MPa (17-to-40 per cent of the hydrostatic pressure) with a median value of 24 per cent. Moreover, even the largest events, like the mainshocks in the 2012–2015 sequence, appear to be triggered by fluid-pressure, similarly as events within swarm sequences. However, while fluid-overpressure decreases with time in an aftershock sequence, it varies randomly at high levels during a swarm sequence. Therefore, based on a fault-valve model, we propose that: 1) the fluids trapped in the fault plane tend toward lithostatic pressure and trigger the mainshock rupture and 2) part of the aftershocks are induced by the diffusing fluid-pressure. On the contrary, swarms need external, likely deep, fluid-pressure feedings. Fluid-pressure is likely to be a common triggering mechanism of the seismicity in the Ubaye Region, even if the involved processes should differ to explain the different types of seismic sequences.

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“…In this context, we can speculate that each mainshock ruptured one of these two OOFs. Such examples have been documented in the literature (e.g., Fojtíková & Vavryčuk, 2018; Noisagool et al., 2016; Singh et al., 2017; Vavryčuk, 2011) and would favor scenario A. Nevertheless, scenario B also remains plausible, that is, stress‐favored, with both M1 and M2 rupturing close to one of the OOFs (within 30° in terms of Kagan angle) with the reactivation of a minor transversal fault of the domino domain, according to the SE side of the L‐shaped aftershock pattern.…”

Section: Discussionmentioning

confidence: 85%

2019 Mw 6.0 Mesetas (Colombia) Earthquake Sequence: Insights From Integrating Seismic and Morphostructural Observations

Poveda

Pedraza

Velandia

et al. 2022

Earth and Space Science

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The boundary between the Northern Andean block and the South American plate is a first‐order tectonic structure in Colombia with historically M > 7 earthquakes. However, details about individual sections of the system remain unknown. We illuminate the seismotectonic of the Algeciras fault by investigating an earthquake sequence that started on 24 December 2019. Using seismic networks at region, we estimate foreshocks and aftershocks focal mechanisms, local stress field, kinematic slip models of the largest events, and Coulomb stress changes. We integrate seismological and morphostructural observations to characterize source properties and reinterpret local faults. Two mainshocks (doublet of Mw 6.0 and 5.8) occurred within 16 min, rupturing just a few kilometers from each other. Discrimination of causative faults among the centroid moment‐tensor nodal planes is difficult because the focal zone is a complex tectonic environment. The focal mechanisms and the local stress field obtained are consistent with a regional NE trending dextral transpressive shear. The relocated aftershocks show a cluster with an L‐shaped pattern concentrated in a ∼7 × 7 km area. Our model defines the Algeciras fault with two structural styles for its northern termination. The NW part is characterized by a duplex‐style of right‐lateral strike‐slip with inner secondary faults of the same sense of movement, and the SE zone by a domino‐style system with inner minor faults of sinistral kinematics. The earthquake doublet is in the zone characterized by the duplex style. In contrast, the southern part of the aftershocks is located in the zone characterized by the domino style.

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Tectonic stress regime in the 2003–2004 and 2012–2015 earthquake swarms in the Ubaye Valley, French Alps

Cited by 19 publications

References 44 publications

Fluid‐Induced Swarms and Coseismic Stress Transfer: A Dual Process Highlighted in the Aftershock Sequence of the 7 April 2014 Earthquake (Ml 4.8, Ubaye, France)

Fluid‐Induced Swarms and Coseismic Stress Transfer: A Dual Process Highlighted in the Aftershock Sequence of the 7 April 2014 Earthquake (Ml 4.8, Ubaye, France)

Swarms and mainshock–aftershocks sequences are both triggered by fluids in the Ubaye Region (Western Alps)

2019 Mw 6.0 Mesetas (Colombia) Earthquake Sequence: Insights From Integrating Seismic and Morphostructural Observations

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