Seismic activity in the Ubaye Region (French Alps): a specific behaviour highlighted by mainshocks and swarm sequences

Baques, Marion; Barros, Louis De; Duverger, Clara; Jomard, Hervé; Godano, Maxime; Courboulex, Françoise; Larroque, Christophe

doi:10.5802/crgeos.76

Cited by 5 publications

(6 citation statements)

References 105 publications

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“…For simplicity, we selected cases of injection-induced seismicity with a single injection borehole interval rather than sites with multiple injections occurring at the same time. For natural swarms, we chose sequences for which fluid involvement is strongly presumed like the Cahuilla swarm (Ross & Cochran 2021) or the Ubaye seismic sequences (Baques et al 2021), and with high-quality (precise locations and magnitudes) earthquake catalogues. For both types of swarms, we did not consider episodes with discontinuous temporal activity or with a complex geological geometry, also for the sake of simplicity.…”

Section: E a Rt H Q Ua K E S C Ata L O G U E Smentioning

confidence: 99%

Inferring fluid volume during earthquake swarms using seismic catalogues

Danré

Barros

Cappa

2022

Geophysical Journal International

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Summary Many studies have pointed out a correlation between either the cumulative or the maximum seismic moment and the injected fluid volume when analyzing global datasets of fluid injection-induced earthquake sequences. However, those correlations become quite uncertain when looking at individual episodes, mainly because of the large aseismic component of the induced deformation. If natural swarms are thought to result from the same physical processes as sequences from anthropogenic origin, little is still known about them as observations are limited by the depth of the active zone and the moderate deformations. In this work, we make profit of the similarity between both natural and injection-induced swarms. To this aim, we develop new relations between seismic observables and hydraulic attributes by using a global compilation of injection-induced earthquake catalogs, leading to two methods to estimate the injected fluid volume based solely on earthquake catalogs. Once the precision of our approaches is validated, we estimate the volume and flowrate of fluids circulating in diverse natural swarms, shedding a new light on the fluid dynamics that trigger them.

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Section: E a Rt H Q Ua K E S C Ata L O G U E Smentioning

confidence: 99%

Inferring fluid volume during earthquake swarms using seismic catalogues

Danré

Barros

Cappa

2022

Geophysical Journal International

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“…2). The seismicity in these two areas behaves differently (Baques et al 2021;Larroque et al 2021). In the Ubaye Valley, the seismicity mainly occurs in clusters (Fig.…”

Section: Seismic Activitymentioning

confidence: 99%

“…The main identified active faults in the Ubaye Region are the High-Durance, the Serenne, and the Jausiers-Tinée faults (Fig. 1; Baques et al 2021;Mathey et al 2020). The first is oriented N-S and is prolonged to the Southeast by the Serenne fault.…”

Section: Tectonic Contextmentioning

confidence: 99%

“…The Ubaye Region, located in the Southwestern Alps, is one of the most seismically active area in France. Mainshock-aftershocks, seismic swarms, and complex sequences have been observed since the 18 th century (Baques et al 2021). In -2004, more than 16,000 events were recorded in a swarm sequence (Jenatton et al 2007;Daniel et al 2011;Leclère et al 2013).…”

Section: Introductionmentioning

confidence: 99%

“…In this study, we aim at better understanding the processes at play, focusing both on the 2014 aftershocks period that was recorded by a dense temporary network (e.g. Baques et al, 2021) and on specific seismic sequences, such as the 2003-2004 seismic swarm and the 2012-2015 seismic crisis, to explain the peculiar seismic behaviour in the Ubaye Region.…”

Section: Introductionmentioning

confidence: 99%

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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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Fluids, faulting and earthquakes in the brittle crust: recent advances and new challenges

Fabbri,

Raimbourg,

Leclère

2024

Comptes Rendus. Géoscience

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Interactions between fluids and deformation are widespread in the brittle crust. As experimentally shown, a high pore fluid pressure p f can fracture intact rocks or reactivate pre-existing fractures. The preference of reactivation over the formation of a new fracture depends on the orientation of the pre-existing fracture with respect to the stress axes and on p f . In nature, the predominant reactivation of misoriented pre-existing faults rather than the formation of new faults with more favorable orientations suggests that pressurized fluids are present in the brittle crust. There is a large body of evidence indicating that supra-hydrostatic p f contributes to the reactivation of lowangle thrust faults or normal faults. Conversely, supra-hydrostatic p f values are less common along vertical or steeply dipping plate boundary transform faults or intra-continental strike-slip faults. If these faults are severely misoriented with respect to the ambient stress field, their reactivation may not be due to supra-hydrostatic p f but to other mechanisms such as shear-enhanced compaction or thermal pressurization. Supra-hydrostatic p f also plays a role in the nucleation or propagation of seismic ruptures in the continental or oceanic crust, and in subducting slabs in convergent margins, as reported for aftershocks, swarms, slow earthquakes, and to a lesser extent for major earthquakes. Lastly, increase or decrease of p f in depth due to human activities such as hydrocarbon extraction, dam impoundment, gas storage or geothermal energy production result in many cases in the inception or enhancement of seismic activiy, adding clues in favor of a relationship between fluids and earthquakes.

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Seismic activity in the Ubaye Region (French Alps): a specific behaviour highlighted by mainshocks and swarm sequences

Cited by 5 publications

References 105 publications

Inferring fluid volume during earthquake swarms using seismic catalogues

Inferring fluid volume during earthquake swarms using seismic catalogues

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

Fluids, faulting and earthquakes in the brittle crust: recent advances and new challenges

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