Examinando por Autor "Hainzl, Sebastian"

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Testing potential trigger mechanisms for seismicity in Sarria‑Triacastela‑Becerrea (Lugo seismic sequences) NW Iberian Peninsula, Spain
(Springer, 2022-10-20) Crespo Martín, Cristina; Martín González, Fidel; Hainzl, Sebastian; Rincón, Marta
The unprecedented and long-lasting seismicity of Triacastela (over 25 years) attracted the interest of the research community on this stable continental region (SCR), particularly after the anomalously high 5.1 and 4.9 Mw earthquakes compared to the regional standards. The high rainfall and tide rates of this region compared to the rest of the Iberian Peninsula, in addition to the recognized existence of thermal springs and crustal fluids, motivated us to test these sources of hydroseismicity as a potential trigger mechanism for the observed seismicity in Triacastela. Based on network upgrades, we have gathered the seismic catalog in two periods for análisis (before and after year 2002). Before 2002, neither a diffusion-type earthquake migration nor any significant statistical correlation between the seismicity rates and rainfall or tides is found. After 2002, some clusters migrate to the south, suggesting the presence of fluid migration during earthquake swarms, but no diffusion-type migration is observed on longer time scales. Furthermore, we find correlation coefficients close to zero, indicating that rainfall and tides can be excluded as driving mechanisms. However, the seismic upward migration, a high b-value (1.2), and a low aftershock-productivity parameter (α = 0.9) observed in this period support the hypothesis of upward fluid migration through fracture zones. The presence of Mantellic helium-3 along the seismogenic faults and the increase of geochemical precursors in the groundwater previously to 1995 and 1997 mainshocks further support deep fluids as a source for the observed induced fluid migration seismicity in Triacastela.
Time-dependent and spatiotemporal statistical analysis of intraplate anomalous seismicity: Sarria-Triacastela-Becerre´a (NW Iberian Peninsula, Spain)
(Oxford Academic, 2021) Crespo Martín, Cristina; Martín-González, Fidel; Yazdi, Pouye; Hainzl, Sebastian; Marta, Rincón
The Sarria-Triacastela-Becerre´a seismicity is located in an intraplate region considered seismically stable, but in 1995 started an unprecedented earthquake activity in the area. Since then an anomalous long-termcontinuous seismicity remains until now in the same location. Despite the long-term seismicity and the large magnitudes for the region standards (5.1Mw), the origin and mechanisms of this seismicity remains unclear. The isolation of background from themain shock–aftershock contribution by means of the application of the Epidemic Type Aftershock Sequences (ETAS) model, the spatial depiction and the resemblance to near seismic regions allow us to identify several seismicity behaviours. From 1995 to 1998/99, the seismicity in this location mainly consists of intensive and deeper earthquake sequences linked to the 1995 and 1997 main shocks. Our results suggest that the main shocks triggered aftershocks and additionally initiated or facilitated aseismic processes. A likely scenario is that the main shocks broke a sealed source at depth allowing a subsequent intrusion of high-pressurized fluids from depth. The resemblance of this period with Zamora seismic characteristics proposes that Triacastela seismicity was also initiated by tectonic activity. From 1998/99 to 2018, a change in seismicity is observed, the background contribution took control and swarm-type activity is predominant. While the earthquake rate decreases, the relative background contribution goes up. Actually, after 2013 the clusters almost disappear and background contribution achieves 55 per cent of the total activity. The spatial migration to the southeast and the upward trend to shallower depth support fluid migration as possible driving mechanism responsible for the transient seismicity in this period. The swarm-type activity in Triacastela in later periods and the resemblance of b-values with Ponte Caldelas and Ventaniella seismicity suggest that the seismicity in Triacastela is related to fluid migration and the reactivation of fractured areas. We propose that the mechanism of this anomalous and long-term seismicity in Triacastela is the mix of different mechanisms, starting with the tectonic seismicity, generated during the 1995 and 1997 seismic sequences, which initiated a fluid upward migration through fractured crustal fault patches, observed after 1998–1999, and responsible for the seismicity during the following 20 yr.