Focal mechanisms of three earthquakes in Finland and their relation to surface faults

Uski, Marja; Hyvönen, Tellervo; Korja, T.; Airo, Meri-Liisa

doi:10.1016/s0040-1951(02)00669-8

Cited by 34 publications

(28 citation statements)

References 24 publications

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“…Fejerskov and Lindholm, 2000;Uski et al, 2003). In-situ stress measurements argue for relatively high magnitudes at shallow depths below the ground surface (Stephansson et al, 1986) The recent discovery of impressive stress-relief structures in different regions of Norway (Roberts, 2000;Roberts and Myrvang, 2004;Pascal et al, 2005) adds support to this conclusion.…”

Section: Seismicity and Stress-fieldmentioning

confidence: 97%

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DynaQlim – Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas

Poutanen

Dransch

Gregersen

et al. 2009

New Frontiers in Integrated Solid Earth Sciences

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The isostatic adjustment of the solid Earth to the glacial loading (GIA, Glacial Isostatic Adjustment) with its temporal signature offers a great opportunity to retrieve information of Earth's upper mantle to the changing mass of glaciers and ice sheets, which in turn is driven by variations in Quaternary climate. DynaQlim (Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas) has its focus to study the relations between upper mantle dynamics, its composition and physical properties, temperature, rheology, and Quaternary climate. Its regional focus lies on the cratonic areas of northern Canada and Scandinavia.Geodetic methods like repeated precise levelling, tide gauges, high-resolution observations of recent movements, gravity change and monitoring of postglacial faults have given information on the GIA process for more than 100 years. They are accompanied by more recent techniques like GPS observations and the GRACE and GOCE satellite missions which provide additional global and regional constraints on the gravity field. Combining geodetic observations with seismological investigations, studies of the postglacial faults and continuum mechanical modelling of GIA, DynaQlim offers new insights into properties of the lithosphere. Another step toward a better understanding of GIA has been the joint inversion of different types of observational data -preferentially connected with geological relative sea-level evidence of the Earth's rebound during the last 10,000 years.Due to the changes in the lithospheric stress state large faults ruptured violently at the end of the last M. Poutanen ( ) Finnish Geodetic Institute, Geodeetinrinne 2, 02430 Masala, Finland e-mail: markku.poutanen@fgi.fi glaciation in large earthquakes, up to the magnitudes M W = 7-8. Whether the rebound stress is still able to trigger a significant fraction of intraplate seismic events in these regions is not completely understood due to the complexity and spatial heterogeneity of the regional stress field. Understanding of this mechanism is of societal importance.Glacial ice sheet dynamics are constrained by the coupled process of the deformation of the viscoelastic solid Earth, the ocean and climate variability. Exactly how the climate and oceans reorganize to sustain growth of ice sheets that ground to continents and shallow continental shelves is poorly understood. Incorporation of nonlinear feedback in modelling both ocean heat transport systems and atmospheric CO 2 is a major challenge. Climate-related loading cycles and episodes are expected to be important, hence also more shortterm features of palaeoclimate should be explicitly treated.

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Section: Seismicity and Stress-fieldmentioning

confidence: 97%

“…The existing studies suggest that the sources are in areas of weakness in the crust which are favourably orientated with respect to the regional stress field and therefore can be reactivated (e.g. Slunga, 1991;Arvidsson and Kulhanek, 1994;Arvidsson, 1996;Uski et al, 2003). Thus studying both aspects (e.g.…”

Section: Seismicity and Stress-fieldmentioning

confidence: 99%

DynaQlim – Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas

Poutanen

Dransch

Gregersen

et al. 2009

New Frontiers in Integrated Solid Earth Sciences

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“…It is somewhat traditional to consider stresses stemming from plate divergence, Alpine convergence, or some other largely horizontal far-field force to constitute an important driver of Fennoscandian seismicity (e.g., Fejerskov & Lindholm, 2000;Uski et al, 2003). However, by definition the European TB must extend from the Barents Sea to the Rockall Trough and beyond (Redfield & Osmundsen, 2013).…”

Section: How Horizontal Is the Force?mentioning

confidence: 99%

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

Redfield¹,

Osmundsen²

2015

NJG

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To a first order, patterns of Fennoscandia's seismicity reflect the benchmark domain boundaries of its Mesozoic rifted margin. Three distinct belts of earthquakes strike sub-parallel to the generalized line of breakup. The outermost seismic belt (SB1) marks the Taper Break (TB), or the zone of flexural coupling/decoupling between the distal (seaward) and proximal/necking (landward) domains. A coastal belt (SB2) follows the Innermost Limit of Extension, defined as the onset of 39 km-thick crystalline continental crust. An interior belt (SB3) follows the Hinterland Break in Slope, or the landward limit of the Scandinavian rifted margin. Between each belt, large portions of the necking, proximal, and hinterland domains are seismically quiescent. Evaluation of the 'Cumulative Seismic Moment' (CSM w ) per unit area indicates that the release of seismic energy is asymmetric. Although some of Fennoscandia's largest seismic events occur in the dominantly Proterozoic to Archean lithosphere of the eastern craton, 80% of Fennoscandian CSM w maps to the domain boundaries of the western rifted margin. CSM w energy tends to be highest at the TB and decreases system atically towards the continental interior.As proposed by many previous studies, a first-order spatial correlation between Scandinavia's offshore earthquake belt and voluminous, geo logically rapid, sedimentary loading during the Neogene period is evident. However, the presence of thinned, faulted crystalline basement is also a very important factor behind Scandinavia's offshore seismicity. Where the Neogene deposits are at their thickest the underlying crust is dominantly oceanic; CSM w is lower per unit area there than where lesser Plio-Pleistocene loading impacts continental crust that was fully prepared by Mesozoic necking and hyperextension. CSM w data suggest that the 'strength' of the TB and the continental margin's distal domain is significantly less than that of relatively young (ca. 54 Ma) oceanic lithosphere. Our data imply that ridge push does not contribute significantly to Fennoscandia's seismicity. Rather, we find that thin-plate bending stresses stemming from offshore depositional loading conspire with unbuttressed Gravitational Potential Energy (GPE), onshore erosion, and post-glacial isostatic rebound to generate Fennoscandia's earthquakes.We present a conceptual seismological model for Fennoscadia that is consistent with modern hypotheses of extended margin evolution, including post-breakup reactivation by footwall uplift in regions adjacent to sharp crustal taper. Illustrated by simple concepts of elastic thin-plate theory, the model honors our conclusion that Fennoscandian seismicity is principally the product of locally derived stress fields and that far field stress from the oceanic domain is unlikely to penetrate deeply into a hyperextended continental margin. It predicts the locations of the observed seismic belts and seismic gaps with the mathematics of thin-plate bending. It describes how the outer seismic belt will remain localized in the...

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“…He used the differential time between Pg and sPg to measure focal depths of a number of earthquakes. Besides this, there are many related stduies on determining the focal depth using local depth phase [16][17][18][19][20][21][22][23][24][25]. In brief, the method of determining the focal depth with depth phase has broad application and this method is very useful especially when the station distribution is spare.…”

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confidence: 99%

A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone

Luo

Zeng

et al. 2010

Sci. China Earth Sci.

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Previous studies show that mature faults are filled with fault gouge in the shallow part and thus cannot accumulate enough strain energy for earthquakes. Therefore most earthquakes are deeper than 5 km, except those events occurring on new faults or in intact rocks. From field observation, Wenchuan earthquake is found to rupture the free surface about 200 km, but the rupture may extend underground much further from teleseismic body waves inversion and aftershocks distribution. In the northeastern end of the rupture zone, deep rupture may induce stress increase near the free surface, and trigger shallow earthquakes. An M s 5.7 aftershock occurred at Qingchuan, northeast end of Wenchuan earthquake fault on July 24, 2008, featuring thrust mechanism with a 3 km source centroid depth. The shallow focal depth is confirmed with the sPL phase recorded at station L0205. As Rayleigh wave is well only developed for source depth less than 1/5 of epicentral distance, the observed large amplitude of Rg at a distance of 15 km implied depth of 3 km or less. Dozens of aftershocks' sPL waveforms are also analyzed to confirm the source depths less than 3 km. On the other hand, no surface ruptures are found by geological survey or InSAR studies. It is strongly suggested that these aftershock sequences initiate fresh rupture in intact rocks triggered by stress increase from the deep co-seismic rupture of the Wenchuan mainshock.Wenchuan earthquake, shallow earthquake, focal depth, wave modeling Citation:Luo Y, Ni S D, Zeng X F, et al. A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone.On May 12, 2008, an M s 8.0 earthquake occurred at Wenchuan, Sichuan Province, and caused heavy economic loss and casualties. Dozens of strong aftershocks with magnitude ≥5.0 occurred along the Longmenshan faults in the following months. The depth and focal mechanism of the aftershock sequence provided a good constraint on mainshock fault and regional stress field. Focal depth is an important parameter to study regional seismicity and seismic hazard, and also plays a particularly important role in understanding the relationship between seismicity and geological structure. Depths of most intraplate earthquakes are between 5 and 25 km [1][2][3][4]. When depth is larger than 25 km, it is not very easy to accumulate strain because of ductile deformation in the lower crust. When depth is less than 5 km, mature faults are filled with soft fault gouge in the upper part; thus, it is difficult to accumulate enough strain. Recent studies show that the depths of Wenchuan earthquake aftershocks are mostly in the range of 5-20 km [5][6][7][8][9][10]. But in many regions, especially inside an old stable intraplate such as southwest part of Australia (Merkering) and North America, nearsurface stress measurements in the area show relatively high deviatoric stress. Because of strong strength in cold and old

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Focal mechanisms of three earthquakes in Finland and their relation to surface faults

Cited by 34 publications

References 24 publications

DynaQlim – Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas

DynaQlim – Upper Mantle Dynamics and Quaternary Climate in Cratonic Areas

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone

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