In this study, we build a multi‐station phase‐picking model named EdgePhase by integrating an Edge Convolutional module with a state‐of‐the‐art single‐station phase‐picking model, EQTransformer. The ...Edge Convolutional module, a variant of Graph Neural Network, exchanges information relevant to seismic phases between neighboring stations. In EdgePhase, seismograms are first encoded into the latent representations, then converted into enhanced representations by the Edge Convolutional module, and finally decoded into the P‐ and S‐phase probabilities. Compared to the standard EQTransformer, EdgePhase increases the precision (fraction of phase identifications that are real) and recall (fraction of phase arrivals that are identified) rate by 5% on our training and test data sets of Southern California earthquakes. To evaluate its performance in regions of different tectonic settings, we applied EdgePhase to detect the early aftershocks following the 2020 M7.0 Samos, Greece earthquake. Compared to a local earthquake catalog, EdgePhase produced 190% additional detections with an event distribution more conformative to a planar fault interface, suggesting higher fidelity in event locations. This case study indicates that EdgePhase provides a strong regional generalization capability in real‐world applications.
Plain Language Summary
Identifying seismic phases from continuous waveforms is an important task for earthquake monitoring and early warning systems. Traditional phase recognition methods include visual inspection and detections based on mathematical functions (e.g., STA/LTA, kurtosis, AIC). Recently, machine learning technology has been applied to this task because of its fast operation speed and complete automation. A variety of neural‐network‐based models take the waveforms of a single station as input and predict the P‐phases and S‐phases. In this study, we improve the model performance by taking into account the mutually consistent features in multiple stations. We incorporate a Graph Neural Network module to exchange information relevant to seismic phases between neighboring stations. Compared to the standard single station model, our multi‐station model performs better on seismic data in Southern California in terms of the precision and recall rate. We also tested our model on the 2020 M7.0 Greece, Samos Earthquake and found that it detected significantly more aftershocks compared to local catalogs in the first month after the mainshock.
Key Points
We developed EdgePhase, a multi‐station phase‐picking model, by fine‐tuning EQTransformer with Graphic Neural Networks
Compared to the standard EQTransformer, EdgePhase increases the F1 score by 5% on the Southern California Seismic data set
Performance evaluation of EdgePhase shows its strong generalization ability in real‐world applications
Due to the unique soil and morphological conditions prevailing in Izmir Bay basin, structural damage has been governed by site effects. Consistently, during October 30, 2020 M7.0 Samos Earthquake, ...which took place offshore of Samos Island, structural damage and life losses were observed to be concentrated in Bayrakli region of Izmir Bay, despite the fact that the fault rupture was at a distance of 65–75 km from the city of Izmir. Additionally, strong ground motions recorded in Izmir Bay showed unique site amplifications that were observed surprisingly at both rock and soil sites. Soil amplifications and duration elongations were mostly due to site effects governed by the response of very deep alluvial deposits of low plasticity. Similarly, due to very extensive faulting-induced fracturing and unusually stratified nature of rock sub-layers, unexpected long period amplifications were also observed at rock sites. These earthquake and site resonance effects were more pronounced in the period range of 0.5–1.5 s. When they were superposed with relatively coinciding natural period of 7–9 story residential buildings of Izmir City, it was concluded that the triple resonance effects among incoming rock ground motions, soil deposits, and the damaged buildings, amplified and prolonged the overall system response. Within the confines of this manuscript, the governing role of site effects leading to increased seismic demand was assessed, through a series of 1D equivalent linear, total stress-based site response assessments, the results of which clearly highlighted the variation of seismic demand in Izmir Bay.
•Samos Island earthquake produced rich long period rock spectral accelerations.•Deep soil sites in Izmir Bay, amplified these long period rich rock motions.•Due to resonance effects, 7-9 story buildings were subjected to larger shakings.•Site effects increased seismic demand and prolonged shaking duration.•These, along with poor design-construction practices caused structural damage.
The seismic, geodetic, and tsunami observations are utilized to investigate the October 30th 2020 Samos, Greece earthquake. We adopt back projection (BP) and multi-point source (MPS) techniques to ...determine the rupture directivity and focal mechanism change of this event. Both methods reveal a unilateral rupture propagation to the west of the epicenter, and also resolve a changed focal mechanism. We use a two-segment-faults geometry to parameterize the fault model with strikes at 283° for the east segment and 250° for the west respectively, and conduct a finite fault inversion (FFI) combining seismic and geodetic observations. The kinematics results indicate the whole rupture process lasts about 25 s, yielding a total seismic moment of 3.16×1019 Nm (Mw = 6.9) with a peak moment rate reaching 3.1×1018 Nm/s around 10 s. The rupture is composed of two asperities separated by the junction of two fault planes. The main slip area, with maximum amplitude reaching three meters, distributes at a shallow depth and displays a complementary pattern with aftershocks. The slip in the first six seconds is dominated by a pure normal faulting mechanism, while the following rupture includes an additional strike-slip component. The change of focal mechanism reflects the tectonic transition from dilatation to lateral shearing, which is also evident in the aftershock mechanisms. The synthetic tsunami waves also well fit three tidal gauge observations. The coseismic Coulomb stress is calculated to analyze the relationship between the mainshock and aftershock evolution. The mechanism combination of two rupture epochs reflects the combination of shear and dilatational stress status and complicated fault system of the Samos source area.
•Segmented rupture of the 2020 Mw 6.9 Samos earthquake is revealed by BP and MPS techniques.•The slip model of the event is constrained by multiple observations.•Tsunami wave simulation over the Agean Sea is performed and validated by tidal gauge observations.
On October 30, 2020, an earthquake with a magnitude of 6.8 (Mw) struck the northern coast of Samos Island in the Kuşadası Gulf. The solution to the focal mechanism indicates that the earthquake of 30 ...October 2020 occurred on a normal fault with nodal planes of E-W strike; thus, indicating extension in N-S direction. The fault plane solutions show a N-S trending extension for normal faults, which are obtained by inverting the moment tensor waveforms of 23 earthquakes and the P-wave first motion polarities of 11 aftershocks. A normal fault stress regime of approximately N-S (N6°E) σ3 axis is given by the inversion of slip vectors measured at sites located on land in Kuşadası. The mean R value is 0.84, suggesting that the stress regime is triaxial extensional stress state. The inversion of the focal mechanism of earthquakes occurring on land and in the Gulf of Kuşadası describes an extensional stress regime active today, characterized by an approximately N-S (N9°E) σ3 axis. The calculated R value of 0.31 indicates a triaxial stress state. For the 30 October 2020 earthquake (Mw:6.8), the Coulomb failure stress change analysis shows a substantial reduction in stress in the N-S direction supporting the kinematic results. The N-S extension in Western Anatolia-Aegean is largely influenced by the relatively fast movement of the Hellenic trench southwards, related to the sinking of the African plate beneath Aegean.
•The Samos Earthquake (M:6.8) of 30 October 2020 shows N-S extensional regime character.•This tectonic regime contributes to the development of the E-W gulfs on the coast of the Aegean.•The N-S extension is due to the relative rapid motion of the Hellenic trench towards the south.•The high rate of movement towards the Hellenic trench is related to the roll-back of African slab.
The October 30, 2020, Mw7 Samos earthquake ruptured a north-dipping offshore normal fault, bounding the Samos basin; it accommodated ∼N-S extension and can be viewed as a modern manifestation of the ...basin evolution. It caused 118 fatalities, generated a tsunami, and caused a co-seismic uplift of 20 to 35 cm of the NW part of Samos Island. Using broadband, strong-motion, and geodetic data, we constrain the location and source geometry of the mainshock. A multiple-point source model suggests three sequential subevents providing 20 s of source duration. Our finite-fault kinematic model confirms the prevalence of large slip amplitudes (∼2.4 m) along the entire ruptured area and the up-dip and westward rupture propagation. This directivity is independently confirmed by Apparent Source Time Functions inferred from regional recordings using a herein developed new variant of the empirical Green's function method. Static GNSS displacements from inland stations yield a near-surface co-seismic slip of ∼1 m amplitude, contributing to any interpretation of the observed island uplift. The 2020 Samos event showed that in the spatially heterogeneous oblique transtentional regions in the back-arc Aegean region, normal faults bounding the basins are capable to rupture in M7 earthquakes, provoke tsunami generation, and constitute a constant threat to the nearby coastal areas of both Greece and Turkey.
•Source complexity of three coseismic episodes, including localized shallow slip•Rupture directivity towards west, resolved from apparent moment rate functions.•Manifestation of twin-basin evolution in oblique transtensional regime
Earthquakes are a consequence of the motions of the planet's tectonic plates, yet predicting when and where they may occur, and how to prepare remain some of the shortcomings of using scientific ...knowledge to protect human life. A devastating Mw 7.0 earthquake on October 30, 2020, offshore Samos Island, Greece was a consequence of the Aegean and Anatolian upper crust being pulled apart by north-south extensional stresses resulting from slab rollback, where the African plate is subducting northwards beneath Eurasia, while the slab is sinking by gravitational forces, causing it to retreat southwards. Since the retreating African slab is coupled with the overriding plate, it tears the upper plate apart as it retreats, breaking it into numerous small plates with frequent earthquakes along their boundaries. Historical earthquake swarms and deformation of the upper plate in the Aegean have been associated with massive volcanism and cataclysmic devastation, such as the Mw 7.7 Amorgos earthquake in July 1956 between the islands of Naxos and Santorini (Thera). Even more notable was the eruption of Santorini 3650 years ago, which contributed to the fall of the Minoan civilization. The Samos earthquake highlights the long historical lack of appreciation of links between deep tectonic processes and upper crustal deformation and geological hazards, and is a harbinger of future earthquakes and volcanic eruptions, establishing a basis for studies to institute better protection of infrastructure and upper plate cultures in the region.
On 30 October 2020, a strong normal-faulting earthquake struck Samos Island in Greece and İzmir Province in Turkey, both in the eastern Aegean Sea. The earthquake generated a tsunami that hit the ...coasts of Samos Island, Greece and İzmir, Turkey. National teams performed two post-tsunami field surveys on 31 October to 1 November 2020, and 4–6 November 2020, along the Turkish coastline; while the former was a quick survey on the days following the tsunami, the latter involved more detailed measurement and investigation focusing on a ~ 110-km-long coastline extending from Alaçatı (Çeşme District of İzmir) to Gümüldür (Menderes District of İzmir). The survey teams measured runup and tsunami heights, flow depths, and inundation distances at more than 120 points at eight different localities. The largest tsunami runup among the surveyed locations was measured as 3.8 m in Akarca at a distance of 91 m from the shoreline. The maximum tsunami height of 2.3 m (with a flow depth of 1.4 m) was observed at Kaleiçi region in Sığacık, where the most severe tsunami damage was observed. There, the maximum runup height was measured as 1.9 m at the northeastern side of the bay. The survey team also investigated tsunami damage to coastal structures, noticing a gradual decrease in the impact from Gümüldür to further southeast. The findings of this field survey provide insights into the coastal impact of local tsunamis in the Aegean Sea.
The 30 October 2020 Samos earthquake (Mw 7.0) ruptured an east–west striking, north dipping normal fault located offshore the northern coast of Samos Island, previously inferred from the bathymetry ...and regional tectonics. This fault, reported in the fault-databases as the
North Samos
and/or
Kaystrios Fault
, ruptured with almost pure dip-slip motion, in a region where both active extension and strike-slip deformation coexist. Historical information for the area confirms that similar ~ Mw7 events had also occurred in the broader Samos area, though none of the recent (last ~ 300 years) mainshocks appears to have ruptured the same fault. The spatial and temporal distribution of relocated aftershocks indicates triggering of nearby strike-slip and normal fault segments, situated in the areas where static stress has increased due to the mainshock generation. The relocated aftershocks and the slip model indicate that the sequence ruptured the upper crust (mainly the depth range 3–15 km). The top of the rupture plane nearly reached the sea bottom, located at a depth of < 1 km. Slip is confined in mainly two asperities, both located up-dip from the hypocenter and at shallow depths. The average displacement is ~ 1 m and the peak slip is ~ 3.5 m for a shear modulus of 3.2e10 N/m
2
. While it is difficult to constrain the rupture velocity in the inversions, the model suggests a slow rupture speed of the order of 2.2 km/s. The resolved source duration is ~ 16 s, compatible with the ~ 32 km length of the fault that ruptured.
The October 30, 2020 Earthquake caused unexpectedly significant damage in İzmir considering its distance to the city. This paper evaluates the recorded ground motions, summarizes the performance of ...structures affected from the earthquake with emphasis on the reasons of damage. A detailed damage assessment was carried out by the Earthquake Engineering Research Center of Middle East Technical University to compile data on the damage of RC and masonry buildings. It was observed that majority of the damage was concentrated in the Bayraklı district due to its peculiar soil properties where many 7–10 story mid-rise RC buildings suffered heavy damage and collapse. The level of amplified ground motions combined with deficiencies of apparently non-code compliant buildings exacerbated the damage. The main reasons of damage were mainly attributed to the presence of soft stories, lack of proper detailing, poor construction quality, presence of heavy overhangs, and hence significant lack of code-compliance in essence. The influence of infill walls on seismic performance of deficient and inadequate buildings was clearly seen in this earthquake. This paper also discusses seismic code requirements in effect and their influence on the observed building performance. The recorded ground motions were compared with the code spectra to evaluate the performance of the buildings. The code response spectra were found to be well above the recorded ground motion spectra at the sites where significant damage was observed.
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
Recenzirano
Odprti dostop
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
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