Microseismicity analysis in the geothermal area of Torre Alfina, Central Italy
A. LisiAlessandro MarchettiA. FrepoliNicola Mauro PagliucaGiuliana MeleMaria Luisa CarapezzaM. CaciagliDaniela FamianiAlessandro GattusoThomas Braun
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Fault plane
The seismicity patterns and parameters in Fuzhou area,especially the characteristics of the swarm of earthquake(M3.8),have been studied in this paper ,we hope to provide a scientific basis for the seismically and shockproof and hazard reducing in the future .
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Fault plane
Principal stress
Echelon formation
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Abstract Fracture and fault zones can channel fluid flow and transmit injection‐induced pore pressure changes over large distances (>km), at which seismicity is rarely suspected to be human induced. We use seismicity analysis and hydrogeological models to examine the role of seismically active faults in inducing earthquakes. We analyze a potentially injection‐induced earthquake swarm with three events above M 4 near the White Wolf fault (WWF). The swarm deviates from classic main aftershock behavior, exhibiting uncharacteristically low Gutenberg‐Richter b of 0.6, and systematic migration patterns. Some smaller events occurred southeast of the WWF in an area of several disposal wells, one of which became active just 5 months before the main swarm activity. Hydrogeological modeling revealed that wastewater disposal likely contributed to seismicity via localized pressure increase along a seismically active fault. Our results suggest that induced seismicity may remain undetected in California without detailed analysis of local geologic setting, seismicity, and fluid diffusion.
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The San Miguel fault system strikes in the northwest direction within the Peninsular Ranges of Baja California. The study concentrates primarily on the southern sector of the San Miguel fault (SSM) which is about 20 km long and had a large rupture in 1956 .
There is a high rate of seismicity along the SSM. In a time period of 23 days, 109 events were located, with duration magnitudes between 1.4 and 2.8. Focal depths are between 5 and 15 km. Epicentral locations show three clusters of seismicity. Two clusters are on the SSM. Another cluster is closer to a normal fault that strikes parallel 8 km to the southwest of SSM. The seismicity is stationary, with an average of 20 events per day. A “ b ” value of 0.92 ± 0.02 is characteristic for the background seismicity. A larger “ b ” value of 1.4 ± 0.07 is associated with the cluster at the northwest end of SSM. Those inconsistent “ b ” values suggest a heterogeneous state of stress .
Most fault plane solutions in the Northern Peninsular Ranges of Baja California indicate strike-slip motions (one normal mechanism is also observed). The greatest principal stress is oriented approximately north-south .
Fault plane
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Seismicity reflects underground stress states, satisfying scaling laws such as Gutenberg-Richter law and Omori-Utsu law. Standard seismicity models based on these scaling laws, such as the Epidemic Type Aftershock Sequence (ETAS) model, are useful to identify swarm anomalies in seismicity catalogs. Llenos et al. (2009) applied the ETAS model to swarms triggered by slow slip events (SSEs) and found that stressing rate controls the background seismicity μ suggesting that swarms can be utilized to monitor stress change due to various aseismic processes. Following their work, we analyze the 2002 and 2007 Boso swarms triggered by the Boso SSEs (Ozawa et al., 2007) and a swarm beneath Tokyo Bay, in June 2005. A single ETAS model cannot explain the high seismicity during a swarm. Although a combination of three ETAS models for pre-swarm, swarm, and post-swarm periods better explains the data, a simpler model with an ETAS model and a boxcar function is even better. Similarity of the seismicity model, together with the locations and focal mechanisms, suggests that three swarms share a common source of stress, and the possibility of undetected SSE beneath Tokyo Bay.
Peninsula
Statistic
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