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Scaling properties of the Mw7.0 Samos (Greece), 2020 aftershock sequence

Vallianatos Filippos, Pavlou Kyriaki

Acta Geophysica

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2021

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Vol. 69, no. 3

1067--1084

EN

On October 30, 2020, a strong and shallow earthquake (Mw=7.0) hit Samos, an island on the eastern edge of the Aegean Sea (Greece). The epicenter was located on the north ofshore of the Greek island of Samos. The goal of our work is to provide a frst analysis of the scaling properties observed in the aftershock sequence as reported until December 31, 2020, as numerous seismic clusters activated. Our analysis is focused on the main of the clusters observed in the East area of the activated fault zone and strongly related with the mainshock’s fault. The aftershock sequence follows the Omori law with a value of p ≈ 1.01 for the main cluster which is remarkably close to a logarithmic evolution. The analysis of interevent times distribution, based on non-extensive statistical physics indicates a system in an anomalous equilibrium with a crossover from anomalous (q>1) to normal (q=1) statistical mechanics, as great interevent times approached. A discussion of the crossover observed, is given in terms of superstatistics. In addition, the obtained value q ≈ 1.67 suggests a system with one degree of freedom. Furthermore, a scaling of the migration of aftershock zone as a function of the logarithm of time is discussed in terms of rate strengthening rheology that govern the evolution of afterslip process.

2

The seismogenic tectonic of Anchorage Mw7.0 Earthquake in Alaska, November, 30, 2018

Lei Dongning, Yang Gang

Acta Geophysica

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2020

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Vol. 68, no. 3

619--626

EN

The Mw7.0 Anchorage earthquake is most signifcant event since 1964 Mw9.2. Far away subduction zone trace, thus the seismogenic structure and failure plane are not clear and keep disputed. Based on published data, including faults, aftershock, focal mechanism solutions and source fault model and so on, we make comprehensive analysis and discussion. We think that this earthquake belongs to plate subduction event, without relationship with Castle Mountain fault and Border Ranges fault for seismogenic structure, only earthquake-controlling structure. Both faults are not responsible for the Anchorage earthquake. The actual seismogenic fault plane has a south-to-north trending and dips to east, which is corresponding to the nodal plane I.

3

Scaling Analysis of Time Distribution between Successive Earthquakes in Aftershock Sequences

Marekova E.

Acta Geophysica

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2016

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Vol. 64, no. 4

885--903

EN

The earthquake inter-event time distribution is studied, using catalogs for different recent aftershock sequences. For aftershock sequences following the Modified Omori’s Formula (MOF) it seems clear that the inter-event distribution is a power law. The parameters of this law are defined and they prove to be higher than the calculated value (2 – 1/p). Based on the analysis of the catalogs, it is determined that the probability densities of the inter-event time distribution collapse into a single master curve when the data is rescaled with instantaneous intensity, R(t; Mth), defined by MOF. The curve is approximated by a gamma distribution. The collapse of the data provides a clear view of aftershock-occurrence self-similarity.

4

The 2014 Kefalonia Doublet (Mw6.1 and Mw6.0), Central Ionian Islands, Greece: Seismotectonic Implications along the Kefalonia Transform Fault Zone

Karakostas V., Papadimitriou E., Mesimeri M., Paradisopoulou P., Gkarlaouni Ch.

Acta Geophysica

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2015

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Vol. 63, no. 1

1--16

EN

The 2014 Kefalonia earthquake sequence started on 26 January with the first main shock (Mw 6.1) and aftershock activity extending over 35 km, much longer than expected from the causative fault segment. The second main shock (Mw 6.0) occurred on 3 February on an adjacent fault segment, where the aftershock distribution was remarkably sparse, evidently encouraged by stress transfer of the first main shock. The aftershocks from the regional catalog were relocated using a 7-layer velocity model and station residuals, and their distribution evidenced two adjacent fault segments striking almost N-S and dipping to the east, in full agreement with the centroid moment tensor solutions, constituting segments of the Kefalonia Transform Fault (KTF). The KTF is bounded to the north by oblique parallel smaller fault segments, linking KTF with its northward continuation, the Lefkada Fault.

5

Aftershocks in modern perspectives: Complex earthquake network, aging, and non-Markovianity

Abe S., Suzuki N.

Acta Geophysica

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2012

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Vol. 60, no. 3

547-561

EN

The phenomenon of aftershocks is studied in view of science of complexity. In particular, three different concepts are examined: (i) the complex-network representation of seismicity, (ii) the event-event correlations, and (iii) the effects of long-range memory. Regarding (i), it is shown that the clustering coefficient of the complex earthquake network exhibits a peculiar behavior at and after main shocks. Regarding (ii), it is found that aftershocks experience aging, and the associated scaling holds. And regarding (iii), the scaling relation to be satisfied by a class of singular Markovian processes is violated, implying the existence of the longrange memory in processes of aftershocks.

6

Podhale, Poland, earthquake of November 30, 2004

Wiejacz P., Dębski W.

Acta Geophysica

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2009

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Vol. 57, no. 2

346-366

EN

Earthquake of November 30, 2004, in Podhale region, southern Poland, was of unexpectedly big size in this area of weak seismicity. As Poland is considered a country of low seismicity, the earthquake has caused concern about seismic hazard in Poland, especially since it took place shortly after the even more unexpected Kaliningrad Region, Russia, earthquakes of September 21, 2004, that inflicted minor damage in northern Poland. The paper presents the findings on the Podhale earthquake which reached macroseismic intensity up to 7 and magnitude 4.7 (mb; ISC). The event was felt up to a distance of about 100 km and inflicted slight damage to buildings in its narrow epicentral area, thus evidencing its relatively shallow depth. The quake has been located near the village of Skrzypne, about 15 km west-southwest of the district capital Nowy Targ. The source mechanism has been found to be of dip slip normal fault type, although a problem remains of association of this mechanism with known tectonic dislocations in the region. The earthquake has been followed by a long series of aftershocks. Their distribution in time is also studied and the biggest aftershocks have been located.

7

Seismicity of the northernmost part of the Red Sea (1995-1999)

Korrat I., Hussein H., Marzouk I., Ibrahim E., Abdel-Fatah R.

Acta Geophysica

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2006

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Vol. 54, no. 1

33-49

EN

Seismicity in the northernmost part of the Red Sea has been studied using data from Hurghada Seismological Network in addition to readings from the existing neighbouring networks. Relocated events in addition to data from national centers are used to obtain a complete and true picture for the seismicity of the area. The spatial distribution of earthquakes defines three earthquake zones in the Gulf of Aqaba and three zones at the entrance of the Gulf of Suez and southern tip of Sinai Peninsula. The thermal activity and the triple junction nature control the activity in this area. The activity defines also an active trend extending from the southern tip of Sinai Peninsula to the median zone of the Red Sea. The seismicity of this trend is probably related to the active spreading zone associated with the opening of the Red Sea. The b-values are derived for the entrance areas of the two gulfs and for Gulf of Aqaba. Values of b are 1.35 for the triple junction region, 1.13 for the activity be-fore the 22 November 1995 Gulf of Aqaba mainshock and 1.25 for the aftershocks of this event.

8

Stress release during earthquake sequences

Gibowicz S.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 3

271-299

EN

The average stress drop and apparent stress released during 65 complex earthquake sequences from all over the world are estimated separately for foreshocks, main shocks and aftershocks. All of them but one occurred between 1977 and 1997. The Harvard CMT solutions are available for 60 main shocks, 38 foreshocks and 218 aftershocks. The stress drop is estimated using the values of seismic moment and source half duration and the scaling relations between various source parameters: seismic moment, source half duration, fault surface and fault length, taken from Harvard catalogues and other publications. The average stress drop is the highest during foreshocks (1.8 MPa), middle during main shocks (1.1 MPa) and the lowest during aftershocks (0.4 MPa). Similarly, the apparent stress, estimated from seismic moment and radiated energy taken from PDE-NEIC bulletins and other publications, is also the highest for foreshocks (0.6 MPa), middle for main shocks (0.4 MPa) and the lowest for aftershocks (0.2 MPa).

9

A search for sequences of mining-induced seismic events at the Rudna Copper Mine in Poland

Kwiatek G.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 2

155-171

EN

A detailed analysis of the Rudna copper mine's seismic catalogue for 1980-2003, with a threshold local magnitude ML> 1.3, allowed to distinguish several types of event sequences related to 345 stronger mining events of magnitude greater than 3.0. Events without aftershocks and foreshocks were observed as well as those where the number of aftershocks numbered more than ten, while foreshocks - several. Foreshocks were recorded for 58 events, nearly all of them several tens of minutes before the main seismic event. Aftershocks accompanied the 190 strongest events; the greatest number of aftershocks was 10 for an event of magnitude just over 3.0. For the two strongest events, of magnitudes ML = 4.1 and ML = 4.2, the number of aftershocks was radically different, 9 and 1, respec-tively. Different numbers of aftershocks were observed depending on the loca-tion of the main event in various mining areas, which is related to the differences in the seismicity of individual zones within the mine. Non-parametric probability distribution functions of magnitude have been determined for the different seismogenic zones. In addition, the value of the b coefficient of the Gutenberg-Richter relation has been analyzed for each zone. These studies confirmed that seismicity varies within the mine.

10

Focal mechanism and source time function of selected aftershocks of the Egion 1995 earthquake, Gulf of Corinth, Greece

Gibowicz S., Domański B., Wiejacz P.

Acta Geophysica Polonica

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1999

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Vol. 47, nr 1

1-25

EN

Numerous aftershocks, which followed the 1995 Egion earthquake of magnitude Ms = 6.2, were recorded by the seismic network PATNET of the University of Patras and by a temporary local network EGINET. The well recorded aftershocks were located by the Patras Seismological Centre, University of Patras. The complete data set, received from the Centre, contains the records of over a hundred events. The spatial distribution of their epicentres forms an E-W elongated cloud with a central cluster and a few stray-away epicentres west and north-west from the cloud. The events from the central cluster, which is the source area of the main shock, that occurred during the first decade of August 1995, were selected for the analysis. Additionally, a few events from the small cluster located west of the main one were also analysed. Altogether, it was possible to perform the moment tensor inversion in the time domain for 29 aftershocks from the main cluster and for 4 events from the small cluster. The selected aftershocks have moment magnitude ranging from 1.7 to 3.2. The source time function of the larger events was determined by the empirical Green's function technique. The records of several pairs of large-small aftershocks, close to each other and with similar focal mechanism, were selected for deconvolution. The source time function was recovered for 5 larger aftershocks from the central cluster and for 3 events from the small cluster. The small number of available stations used for the moment tensor inversion limit stable results to the constrained double couple solutions. The solutions show a mixture of various types of the focal mechanism, though dip-slip events prevail over strike-slip events, and normal faulting prevails over reverse faulting. The pulse widths of relative source time functions depend on the station azimuth, indicating that the ruptures propagated unilaterally. The azimuth of rupture direction ranges from about 90 to 250 degrees with the dominant direction of about 200 degrees. The fracture velocity ranges from 0.4 to 0.8 of the shear wave velocity. The obtained results indicate complexity of the stress distribution in the source area of the Egion earthquake.