Megathrust earthquake swarms indicate frictional changes which delimit large earthquake ruptures

SUMMARY When a seismic rupture starts, the process may evolve into multiple ways, generating different size earthquakes. Contrasting models have been proposed to describe the evolution of the rupture process while limited observations at the scale of real earthquake data are available, so that a unifying theory is still missing. Here we show that small and large earthquake ruptures are different before the arrest and they do not exhibit a common, size-independent, universal behaviour. For earthquakes with magnitude 4 < M < 9 occurred in Japan, we measure the initial rate of the P-wave peak amplitude and show that this quantity is correlated to the final event magnitude and not affected by distance attenuation, thus being a proxy for the initiation time of the rupture process. While opening new views on the rupture preparation process, our findings can have significant implications on the effective development of fast and reliable methods for source characterization and ground shaking prediction.

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Shallow megathrust earthquake ruptures betrayed by their outer-trench aftershocks signature

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2017.12.006 ◽

2018 ◽

Vol 483 ◽

pp. 105-113 ◽

Cited By ~ 16

Author(s):

Anthony Sladen ◽

Jenny Trevisan

Keyword(s):

Megathrust Earthquake ◽

Earthquake Ruptures

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Large slip, long duration, and moderate shaking of the Nicaragua 1992 tsunami earthquake caused by low near-trench rock rigidity

Science Advances ◽

10.1126/sciadv.abg8659 ◽

2021 ◽

Vol 7 (32) ◽

pp. eabg8659

Author(s):

Valentí Sallarès ◽

Manel Prada ◽

Sebastián Riquelme ◽

Adrià Meléndez ◽

Alcinoe Calahorrano ◽

...

Keyword(s):

Large Earthquake ◽

Rock Properties ◽

Long Duration ◽

Consistent Model ◽

Finite Fault ◽

Earthquake Ruptures ◽

Seafloor Deformation ◽

Tsunami Earthquake ◽

Elastic Rock ◽

Earthquake Characteristics

Large earthquake ruptures propagating up to areas close to subduction trenches are infrequent, but when they occur, they heavily displace the ocean seafloor originating destructive tsunamis. The current paradigm is that the large seafloor deformation is caused by local factors reducing friction and increasing megathrust fault slip, or prompting the activation of ancillary faults or energy sources. As alternative to site-specific models, it has been proposed that large shallow slip could result from depth-dependent rock rigidity variations. To confront both hypotheses, here, we map elastic rock properties across the rupture zone of the MS7.0-MW7.7 1992 Nicaragua tsunami earthquake to estimate a property-compatible finite fault solution. The obtained self-consistent model accounts for trenchward increasing slip, constrains stress drop, and explains key tsunami earthquake characteristics such as long duration, high-frequency depletion, and magnitude discrepancy. The confirmation that these characteristics are all intrinsic attributes of shallow rupture opens new possibilities to improve tsunami hazard assessment.

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Earthquake swarms in Greenland

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v31.4665 ◽

1969 ◽

Vol 31 ◽

pp. 75-78

Author(s):

Tine B. Larsen ◽

Peter H. Voss ◽

Trine Dahl-Jensen ◽

Hans Peter Rasmussen

Keyword(s):

Earthquake Swarm ◽

Sedimentary Basins ◽

Large Earthquake ◽

Earthquake Swarms ◽

Intraplate Earthquake ◽

Aftershock Activity ◽

East Greenland ◽

North East ◽

Geological Boundaries ◽

Swarm Activity

Two earthquake swarms have been detected in Greenland. One occurred on the island of Disko in August 2010, the other one was active from January 2008 to June 2009 near the South-East Greenland coast c. 200 km south of Tasiilaq. An earthquake swarm is defined as a series of earthquakes of similar magnitude located within a small area. The magnitude of the largest earthquakes in a swarm is typically less than 4 (Ma & Eaton 2009). Swarm activity is distinctly different from the more common mainshock–aftershock activity, which is characterised by one large earthquake (mainshock) followed by a series of smaller aftershocks. Earthquake swarms mainly occur in areas with tectonic and/or volcanic activity (Stykes 1970), but intraplate swarms are also found in otherwise stable environments (Gregersen 1979; Atakan et al. 1994; Uski et al. 2006; Ma & Eaton 2009). Geological boundaries and old fault zones appear to be a common setting for intraplate earthquake swarms. Earthquake swarms have previously been detected in North and North-East Greenland (Gregersen 1979) at a time when the seismograph coverage was very sparse. It was concluded that the earthquake swarms were caused by tectonic stresses in and around old sedimentary basins near the continental margin.

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