Modeling of Continental Normal Fault Earthquakes Muldashev, Iskander A.; Pérez‐Gussinyé, Marta; Sobolev, Stephan V.
Geochemistry, geophysics, geosystems : G3,
December 2022, 2022-12-00, 20221201, 2022-12-01, Letnik:
23, Številka:
12
Journal Article
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The magnitude of earthquakes on continental normal faults rarely exceeds 7.0 Mw. However, because of their vicinity to large population centers they can be highly destructive. Long recurrence time, ...relatively small deformations, and limited observations hinder our understanding of the deformation patterns and mechanisms controlling the magnitude of events. Here, this problem is addressed with 2D thermomechanical modeling of normal fault seismic cycles. The 2020 Samos, Greece Mw7.0 earthquake is used as an example as it is one of the largest and most studied continental normal fault earthquakes. The modeling approach employs visco‐elasto‐plastic rheology, compressibility, free surface, and a rate‐and‐state friction law for the fault. Modeling of the Samos earthquake suggests the pore fluid pressure ratio on the fault ranges from 0 to 0.7. The model demonstrates that most of the deformation during interseismic and coseismic periods, besides on the fault, occurs in the hanging wall and footwall below the seismogenic part of the fault. The largest vertical surface displacement during the earthquake is the subsidence of the hanging wall in the vicinity of the fault, while the uplift of the footwall and remote part of the hanging wall is significantly smaller. Modeling of the seismic cycles on normal faults with different setups shows the dependency of the magnitude on the thermal profile and dipping angle of the fault; low heat flow and low dipping angle are favorable conditions for the largest events, while steep normal faults in the areas of high heat flow tend to have the smallest magnitudes.
Key Points
We use numerical modeling to investigate continental normal fault earthquakes, using the 2020 Samos Mw7.0 earthquake as an example
Most of the deformation during the seismic cycle, besides on the fault, occurs in the crust below the seismogenic part of the fault
Low dipping angle and low heat flow favor larger magnitudes of normal fault earthquakes
On October 30, 2020 14:51 (UTC), a moment magnitude (M) 7.0 (USGS, EMSC) earthquake occurred in the Aegean Sea. This paper presents the reconnaissance findings regarding the site effects on recorded ...strong ground motion intensities and duration, along with the resulting induced-structural damage in Izmir Bay and Samos Island, respectively. In all rock records, relatively high intensity long period rock spectral accelerations were observed in the mid to long period range of 0.5–1.5 s, which are attributed to the source, more specifically, to the slower rupture-mechanism of the event. These rich spectral intensities were further amplified by soil site effects and soil-superstructure resonance, leading to two to six times amplified overall responses and prolonged seismic shaking durations, more pronounced in Bayrakli and other Izmir Bay sites in Turkey. However, these amplified and prolonged excitations are still below design basis earthquake levels, which addresses the lack of proper structural design and construction deficiencies, as the underlying causes for the collapse to heavy damage performance of 795 buildings. On the other hand, although located only about 10 km from the rupture (22 km from the epicenter) and within the near fault zone, the town of Vathy on Samos Island (Greece) was rather lightly affected by the earthquake, with relatively few collapsed or heavily damaged buildings, partially attributed to the low height/low weight of structures in the area. However, a concentration of damage in low-rise buildings in Ano Vathy hill is considered indicative of a combination of coupled valley and topography effects on the strong motion. This event once again addressed the need to develop region-specific zonation and provisions, when more general code practices are proven to be inadequate to assess these extreme site effects.
We present a comprehensive analysis of pre-seismic anomalies as computed from the ground and space-based techniques during the recent Samos earthquake in Greece on 30 October 2020, with a magnitude M ...= 6.9. We proceed with a multi-parametric approach where pre-seismic irregularities are investigated in the stratosphere, ionosphere, and magnetosphere. We use the convenient methods of acoustics and electromagnetic channels of the Lithosphere–Atmosphere–Ionosphere-Coupling (LAIC) mechanism by investigating the Atmospheric Gravity Wave (AGW), magnetic field, electron density, Total Electron Content (TEC), and the energetic particle precipitation in the inner radiation belt. We incorporate two ground-based IGS GPS stations DYNG (Greece) and IZMI (Turkey) for computing the TEC and observed a significant enhancement in daily TEC variation around one week before the earthquake. For the space-based observation, we use multiple parameters as recorded from Low Earth Orbit (LEO) satellites. For the AGW, we use the SABER/TIMED satellite data and compute the potential energy of stratospheric AGW by using the atmospheric temperature profile. It is found that the maximum potential energy of such AGW is observed around six days before the earthquake. Similar AGW is also observed by the method of wavelet analysis in the fluctuation in TEC values. We observe significant energetic particle precipitation in the inner radiation belt over the earthquake epicenter due to the conventional concept of an ionospheric-magnetospheric coupling mechanism by using an NOAA satellite. We first eliminate the particle count rate (CR) due to possible geomagnetic storms and South Atlantic Anomaly (SAA) by the proper choice of magnetic field B values. After the removal of the statistical background CRs, we observe a significant enhancement of CR four and ten days before the mainshock. We use Swarm satellite outcomes to check the magnetic field and electron density profile over a region of earthquake preparation. We observe a significant enhancement in electron density one day before the earthquake. The parameters studied here show an overall pre-seismic anomaly from a duration of ten days to one day before the earthquake.
On 30 October 2020, an Mw 6.9 normal faulting earthquake occurred off the northern coasts of Samos Island, Greece. The earthquake with moderate magnitude generated the largest tsunami in the eastern ...Mediterranean since the 1956 Amorgos event. Here, we investigate the earthquake source characteristics and examine the factors contributing to the exacerbated tsunami using an integrated approach, including the source inversion from InSAR and GPS data, tsunami simulation, and spectral analysis of tsunami waveforms. The results show that a set of conjugate faults, determined in this study, can explain the geodetic surface deformation equally well. Our tsunami modeling results indicate that the shallow north‐dipping fault was most likely responsible for the mainshock. With the key features of our preferred source models, we infer that the tsunami was intensified by several conditions: (a) the spatial distribution of major coseismic slips coincided with the deepest portion of the Samos Basin which served as an energy reservoir for the tsunami generation; (b) the tsunami was generated in a semi‐closed bay which trapped most of the tsunami energy; (c) the east‐west orientation of the mainshock fault and the location of the concentrated coseismic slips directed the majority of the tsunami energy toward Sığacık Bay, which formed the extremely high tsunami of 3.8 m; (d) the primary tsunami wave period, close to natural oscillation frequency of the harbor, resulted in the observed significant oscillation. We conclude that the tsunami of the 2020 Samos earthquake was exacerbated by both the source characteristics and tsunami resonance property.
Plain Language Summary
Tsunamis are generally generated by megathrust earthquakes in subduction zones, like the 2004 Mw 9.1 Sumatra‐Andaman earthquake. However, a normal‐faulting earthquake on 30 October 2020, in the Aegean Sea generated the largest tsunami in the eastern Mediterranean since 1956. We investigate how the Mw 6.9 normal earthquake could produce tsunami waves of up to 3 m in height and lead to such severe tsunami damage on the coasts of Izmir, Turkey and Samos Island, Greece. We explore the earthquake source characteristics and the factors exacerbating the effects of the tsunami. We evaluate six representative fault models derived from this study and others by comparing their capability of reproducing the observational data, from which we infer the most likely source features. We also analyze the period components of tsunami waveforms to examine how local bathymetry affects the tsunami behavior. We find that the shallow depth of the earthquake with concentrated slips in the deepest water area of the Kuşadası bay is the key factor in producing adequate initial tsunami energy. The tsunami period coincides with the characteristic oscillation periods of the local bays, causing larger tsunami amplitude and longer duration.
Key Points
We find the key features of the tsunami source of the 2020 Samos Earthquake which can best explain a variety of observations
We identify the favorable conditions which contribute to the exacerbated tsunami hazard in the Kuşadası Bay
Tsunamigenic potential of active faults located in confined sea areas may pose unique tsunami hazard and deserves more attention
Many histories of Ancient Greece center their stories on Athens, but what would that history look like if they didn’t? There is another way to tell this story, one that situates Greek history in ...terms of the relationships between smaller Greek cities and in contact with the wider Mediterranean. In this book, author Joshua P. Nudell offers a new history of the period from the Persian wars to wars that followed the death of Alexander the Great, from the perspective of Ionia. While recent scholarship has increasingly treated Greece through the lenses of regional, polis, and local interaction, there has not yet been a dedicated study of Classical Ionia. This book fills this clear gap in the literature while offering Ionia as a prism through which to better understand Classical Greece. This book offers a clear and accessible narrative of the period between the Persian Wars and the wars of the early Hellenistic period, two nominal liberations of the region. The volume complements existing histories of Classical Greece. Close inspection reveals that the Ionians were active partners in the imperial endeavor, even as imperial competition constrained local decision-making and exacerbated local and regional tensions. At the same time, the book offers interventions on critical issues related to Ionia such as the Athenian conquest of Samos, rhetoric about the freedom of the Greeks, the relationship between Ionian temple construction and economic activity, the status of the Panionion, Ionian poleis and their relationship with local communities beyond the circle of the dodecapolis, and the importance of historical memory to our understanding of ancient Greece. The result is a picture of an Aegean world that is more complex and less beholden narratives that give primacy to the imperial actors at the expense of local developments.
On October 30th, 2020, a magnitude 7.0 earthquake offshore off the northern coast of Samos, Greece, generated a tsunami that impacted the nearshore Greek islands and the Aegean coastline of Turkey. ...Here, we describe detailed results from several post-event field surveys, and report first wave arrival timing and polarity information as well as tsunami height/runup measurements, from five islands. In Chios, wave runup reached 1.38 m, in Samos ~ 3 m, in Fourni 1.57 m, in Thimena 1.46 m, and in Ikaria 1.18 m. This event marks two milestones. One, the General Secretariat for Civil Protection of Greece, disseminated a message through Greece's 1–1-2 Emergency Communications Service to all cell phones in the eastern Aegean geographical region, warning recipients to stay away from coastal areas. According to eyewitnesses, the message was received ~ 3–5 min prior to the second and largest flood in Vathi, as the first flood had not sufficiently alarmed the local authorities to evacuate residents. Two, we were able to infer complete tsunami hydrographs from measurements for the first two floods in Vathi, which suggests that the water level rose to about one meter overland flow depth in one minute.
Numa época em que a desinformação é abundante aos nossos sentidos, via meio digital, sempre ressurgem questionamentos baseados em evidências frágeis que não se sustentam como o terraplanismo. ...Todavia, respostas contundentes podem ser resgatadas pela ciência em especial a Física e a Astronomia, originadas desde uma época em que a razão passou a fazer parte da cultura humana. Essa resposta pode surgir dos trabalhos de Eratóstenes e Aristarco de Samos, personagens icônicos da ciência da antiguidade, no cálculo da circunferência terrestre, seu diâmetro e do diâmetro lunar. É isso o que pretendemos mostrar, o trabalho de um (Eratóstenes) servirá de base para o trabalho do outro (Aristarco). Mesmo tendo passado milênios, os resultados, mas principalmente a técnica que eles desenvolveram continua válido.
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•Damage survey conducted on poorly performed 140 reinforced concrete buildings.•The deficiencies in buildings leading to extensive damage were identified.•Most of the collapsed ...buildings suffered ground floor failures due to soft story.•The decisive role of infill walls on the seismic performance of the RC buildings was observed.•Local soil conditions and basin effects amplified the ground motion leading to localized damage.
On October 30th 2020, offshores of Samos Island, Greece was hit by a shallow earthquake of Mw = 6.9 moment magnitude. Located 76 km away from the earthquake’s epicenter, the mid-rise reinforced concrete (RC) building stock of the densely populated Izmir Bayrakli district experienced the most severe structural damage. Although the horizontal peak ground acceleration recorded at the site (PGA = 0.11 g) was well below design values recommended by the past and the present Turkish seismic codes, many buildings suffered heavy damage and 12 buildings collapsed, resulting in a death toll of 117. This paper aims to identify the seismic performance of mid-rise infilled RC frame buildings in Bayrakli by investigating the ground motion recordings, local soil conditions, characteristics of the building stock and the observed damages. The structural performance of 140 RC buildings between 7 and 12 stories that have exhibited poor performance during the earthquake was inspected in detail based on the field surveys conducted right after the earthquake. A database was created documenting the number of stories, major seismic deficiencies, date of construction, geographic coordinates, damage state of structural members and masonry infill walls of the inspected buildings. The localization of structural damage could be partially attributed to the amplified long-distance seismic waves for 0.5–1.5 s periods range due to local soil conditions and basin effects. Seismic vulnerabilities, structural deficiencies and construction quality of the buildings played a significant role in the experienced damage intensity. The influence of infill walls on the seismic performance of RC frame buildings is also clearly observed for code-compliant as well as aseismic buildings.
Four species of the genus Pseudamnicola (Gastropoda: Hydrobiidae Stimpson, 1865), i.e. P. stasimoensis n. sp., P. lesbosensis n. sp., P. samosensis n. sp. and P. skalaensis n. sp are described as new ...to science. The type localities of 13 Pseudamnicola spp. and 1 subspecies hitherto known from Greece, including the Greek part of Cyprus, are presented on a map.
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