On the Statistical Significance of Foreshock Sequences in Southern California

Ende, Martijn van den; Ampuero, Jean‐Paul

doi:10.1029/2019gl086224

Cited by 26 publications

(16 citation statements)

References 19 publications

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“…This is true throughout the years 2010–2015, with few exceptions when a small sequence starts along Pf (February 2011, February 2012, and March 2013). The cumulative number of earthquakes beneath Cf is steady over the years and characterizes the background seismicity with small increments over temporal fluctuations (van den Ende & Ampuero, 2020).…”

Section: The 2009–2016 Sequencesmentioning

confidence: 99%

Seismicity Rate Changes and Geodetic Transients in Central Apennines

Vičič

Aoudia

Borghi

et al. 2020

Geophysical Research Letters

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Using template matching and GPS data, we investigate the evolution of seismicity and observable deformation in Central Apennines. Seismicity appears more persistent at the base of the seismogenic layer than in the shallower crust. Diffuse activity is reported on segments at depth, alternating along strike with apparent quiescence on segments that experienced one or more Mw6+ earthquakes in 1997, 2009, and 2016. Central Apennines are likely underlain by a sizeable shear zone with areas of diffuse seismicity bounding shallow normal faults where Mw6+ earthquakes occurred. The deformation observed at the surface seems to follow the seismicity variations at the base of seismogenic layer along the Apenninic chain. Principal and independent component analyses of GPS data exhibit a transient when the 2016 foreshock sequence starts. This transient propagated northward from the Campotosto fault up to the Alto Tiberina fault system and has likely loaded the Mw6+ 2016 earthquake sequence. Plain Language Summary We use a nonstandard method for the detection of microseismicity at depth augmenting the available catalog. The enhanced seismicity distribution is coupled with the observable deformation on a geodetic network of continuous GPS to infer a better comprehension of the earthquake behavior. The earthquake patterns in Central Apennines reveal a segmentation at depth along an almost flat base of seismogenic layer with alternating low and high seismicity rate segments. The deformation recorded at the surface seems to follow the seismicity variations at the base of seismogenic layer along the Apenninic chain also determining a possible seismic-aseismic mode. We suggest that aseismic deformation has a fundamental role in the tectonic loading and that seismicity, even if heterogeneously distributed, could represent a tracer of it. This conclusion is also supported by the evidence of a transient propagating from south to north during the 2016 Central Italy sequence.

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Section: The 2009–2016 Sequencesmentioning

confidence: 99%

Seismicity Rate Changes and Geodetic Transients in Central Apennines

Vičič

Aoudia

Borghi

et al. 2020

Geophysical Research Letters

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“…Capability to recognize foreshocks before the occurrence of a large event is fundamental for risk monitoring and reduction. There is a large debate in the seismological community on precursory seismicity before a large event and contrasting results have been obtained in indicating the occurrence of foreshock sequences as a persistent feature of moderate to large events (see for California [17,18]). Nevertheless, when a sequence clearly evolves to a large event, foreshocks emerge only when high-resolution seismic catalogs are available, with a magnitude of completeness much smaller than the one presently available for standard monitoring networks.…”

Section: Introductionmentioning

confidence: 99%

Insights into Mechanical Properties of the 1980 Irpinia Fault System from the Analysis of a Seismic Sequence

et al. 2021

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Seismic sequences are a powerful tool to locally infer geometrical and mechanical properties of faults and fault systems. In this study, we provided detailed location and characterization of events of the 3–7 July 2020 Irpinia sequence (southern Italy) that occurred at the northern tip of the main segment that ruptured during the 1980 Irpinia earthquake. Using an autocorrelation technique, we detected more than 340 events within the sequence, with local magnitude ranging between −0.5 and 3.0. We thus provided double difference locations, source parameter estimation, and focal mechanisms determination for the largest quality events. We found that the sequence ruptured an asperity with a size of about 800 m, along a fault structure having a strike compatible with the one of the main segments of the 1980 Irpinia earthquake, and a dip of 50–55° at depth of 10.5–12 km and 60–65° at shallower depths (7.5–9 km). Low stress drop release (average of 0.64 MPa) indicates a fluid-driven initiation mechanism of the sequence. We also evaluated the performance of the earthquake early warning systems running in real-time during the sequence, retrieving a minimum size for the blind zone in the area of about 15 km.

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“…This implies that small and large earthquakes are fundamentally different and the aseismic slip size determines the nucleation length, which scales with the final earthquake magnitude (Ellsworth & Beroza, 1995;Kato et al, 2012;Ruiz et al, 2014Ruiz et al, , 2017. Alternatively, numerous studies suggest that small and large earthquakes start the same way and it is difficult to predict the eventual earthquake magnitude or how the rupture would evolve based on the foreshocks or the P-wave onsets (Ide, 2019;Kilb et al, 2000;Meier et al, 2017;Okuda & Ide, 2018;Uchide & Ide, 2010;Yoon et al, 2019). These observations hint that small earthquakes can directly trigger other earthquakes by transferring stress and eventually leading to the mainshock when the stress or strength condition is favorable for continuous rupture propagation, the cascade model (Ide & Aochi, 2005;McLaskey, 2019;Lui & Lapusta, 2016).…”

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confidence: 99%