Magnitude Mw Research Articles

Deep Blind Fault Activity—A Fault Model of Strong Mw 5.5 Earthquake Seismogenic Structures in North China

North China is one of the high-risk areas for destructive and strong earthquakes in mainland China and has experienced numerous strong historical earthquakes. An earthquake of magnitude MW 5.5 struck Pingyuan County, Dezhou city, in Shandong Province, China, on 6 August 2023. This earthquake was the strongest in the eastern North China Craton since the 1976 Tangshan earthquake. Since the earthquake did not produce surface ruptures, the seismogenic structure for fault responsible for the Pingyuan MW 5.5 earthquake is still unclear. To reveal the subsurface geological structure near the earthquake epicenter, this study used high-resolution two-dimensional (2D) seismic reflection profiles and constructed a three-dimensional (3D) geometric model of the Tuqiao Fault by interpreting the faults in the seismic reflection profiles. This study further combined focal mechanism solutions, aftershock clusters, and other seismological data to discuss the seismogenic fault of the Pingyuan MW 5.5 earthquake. The results show that the Tuqiao Fault is not the seismogenic fault of the MW 5.5 earthquake. The actual seismogenic structure may be related to the NE-oriented high-angle strike-slip blind fault developed in the basement. We further propose three possible fault models for the strong seismogenic structure in North China to discuss the potential seismotectonics in this region.

SOIL LIQUEFACTION HAZARD ASSESSMENT OF DALAMAN RESIDENTIAL AREA

The Phenomenon of Liquefaction gained importance after the 1964 Alaska and Niigata Earthquakes, and it has started to be studied worldwide. Türkiye, located in a very tectonically active zone, has been exposed to many devastating earthquakes. Dalaman is located in SW Anatolia which is under the control of active extensional tectonic regime that may generate such devastating earthquakes in the future. Moreover, because the Dalaman residential area is located on sedimentary deposits, determination of the liquefaction susceptibilities of the soils in the region is an important task to take essential precautions. Analyses have been performed according to two earthquake scenarios with magnitudes Mw=5.5 and Mw=7.5. Standard Penetration Test blow number-based simplified procedure has been used in the analyses and it has been seen that Dalaman residential area is highly susceptible to liquefaction. Most of the liquefiable soils are sands and they make the central part of the area. The northern part of the basin is formed of gravels and safer compared to the southern part, which is formed mostly of sands, silts and clays. Considering the population of the residential area approximately 40.000 people are under danger in case of a M=7.5 earthquake scenario.

Direct Dynamic Triggering Scenarios of the Southern San Andreas Fault by Moderate-Magnitude Cross-Fault Earthquakes in the Brawley Seismic Zone, California

Abstract Intersections between small faults and larger faults are ubiquitous throughout the world, including the strike-slip San Andreas system in southern California. In particular, orthogonal intersections may exist in the Brawley seismic zone (BSZ) in the Salton Sea region between small left-lateral strike-slip faults and the main southern San Andreas fault (SSAF). This area often experiences earthquake swarms, which poses the question of whether moderate earthquakes on these left-lateral cross faults (CFs) may propagate to the nearby SSAF, triggering a large, damaging event. To address this question, we present a collection of dynamic rupture scenarios describing the interaction of a representative CF intersecting the highly prestressed SSAF in the BSZ. Our models span a variety of CF earthquake rupture scenarios that vary in magnitude (Mw∼5.2–6.1), rupture depth, location, and directivity to test their potential to trigger the SSAF. We use our models to investigate how the above parameters play an interconnected role in developing ruptures that might trigger the SSAF. Our results highlight that adjacency to the SSAF and shallow rupture enhance the ability of moderate-size CF earthquakes to propagate onto the SSAF. We also show that earthquakes starting at the opposite edge of the CF from the intersection are less likely to trigger the SSAF unless they propagate over at least half of the CF length. Our experiments provide for the first time a benchmark of comparison and insights into rupture parameters that might control the initiation of a significant SSAF event from a smaller CF earthquake. They may also give insight into the general interactions of small faults with larger intersecting faults, such as in the case of the recent 2023 Kahramanmaraş, Türkiye, earthquake.

Geostatistical Analysis of Lineament Domains: The Study Case of the Apennine Seismic Province of Italy

Regional-scale swarms of subparallel linear topographic features, known as lineament domains, are a common feature of planetary surfaces. Lineament domains are superficial manifestations of the crustal stress field trajectory. Notably, one of the effects of active tectonics is seismicity. Italy is one of the most seismically active regions in the Mediterranean, with many destructive earthquakes that have occurred in past centuries. Here, we assess the seismic meaning of the main lineament domain in the tectonically active region of Central Italy. We describe the use of an automated analysis of satellite imagery coupled with spatial grid analysis to identify three lineament domains of the Central Apennines. Spatial and azimuthal comparisons of the main lineament domain (i.e., the Apennine Domain), with the known locations of earthquakes (moment magnitude of Mw > 5.5) that occurred during the past century, revealed the most seismically active tectonic areas and their spatial distributions. Further, we present a conceptual seismo-geodynamic model for the Central Apennines, which is characterized by regional arching and explains the presence of an extensional tectonic regime in the upper crustal layer of the active Apennines fold-and-thrust belt.

Thoughts of the February 20, 2023 Defne aftershock

On February 6 2023, two large earthquakes with magnitudes of Mw 7.8 (Pazarcık) and Mw 7.6 (Elbistan) occurred consecutively along the East Anatolian Fault Zone in eastern Turkey, causing enormous casualties and heavy damage. This devastating sequence of earthquakes was followed by the Defne aftershock on February 20 near Antakya province, which increased the damage and loss of life. Here, the teleseismic broadband P velocity waveforms are inverted to obtain the coseismic finite-fault slip distribution of the February 20, 2023 Defne aftershock. It was found that the rupture was controlled by the failure of a single asperity with the largest displacement of approximately 0.75 m, which occurred between 6 and 20 km depth. The source mechanism indicated a dominant left-lateral faulting with a significant normal component and released a total seismic moment of 5.85x1018 Nt.m. Coseismic Coulomb stress changes modelling showed that the Defne aftershock rupture was triggered by the earthquake sequence and that the February 6 Pazarcık earthquake had a dominant effect. In the stress modelling carried out on the Dead Sea Fault, the northern segment of the fault remained in the region of significant positive stress loading. Considering the positive stress load over 1 bar created by the earthquake sequence and the Defne aftershock ruptures, as well as the fact that no major earthquake has occurred for more than 600 years, it is clear that the probability of rupture in the northern part has increased significantly and the seismic hazard is high.

Earthquake-triggered ground-failure inventory associated with the M7.1 2018 Southcentral Alaska earthquake

The 30 November 2018, magnitude (Mw) 7.1 earthquake in Southcentral Alaska triggered substantial landslides, liquefaction, and ground cracking throughout the region, resulting in widespread geotechnical damage to buildings and infrastructure. Despite a challenging reconnaissance and remote-sensing environment, we constructed a detailed digital inventory of ground failure associated with the event from several sources. Sources included information derived from remotely sensed data, and data compiled from literature, social media postings, and earthquake damage information compiled by local, state, and federal agencies. Each instance of ground failure within the inventory contains information on the location and type of observed ground failure, and the methods and data used to document the occurrence. Where high-quality data, such as LIDAR or satellite imagery, were available and showed the ground-failure instance clearly, the extent is mapped as a polygon or polyline. All other locations are mapped as points. There are a total of 886 ground-failure instances documented within the inventory (400 landslides, 286 liquefaction features, and 200 features unattributed to specific processes). A semi-quantitative confidence scheme is used to describe mapping certainty associated with each ground-failure feature. This inventory represents a relatively moderate ground-failure-triggering event that occurred in a subarctic environment. This data paper describes the content within the inventory, the inventory data collection procedures, and limitations of the data. Events of this type are not often documented in detail; thus, adding the inventory data to the US Geological Survey Open Repository of Earthquake-Triggered Ground-Failure Inventories further diversifies the datasets available to the scientific community to be used to better understand and model earthquake-triggered ground failure.

The 2022 Mw 6.6 Menyuan earthquake: An early-terminated runaway rupture by the complex fault geometry

The 2022 Mw 6.6 Menyuan earthquake, which caused unexpectedly large surface offsets (about 2.6–3.5 m) relative to the moment magnitude of this event, is one of the best-recorded strike-slip events in the northeastern Tibetan plateau. Although previous studies have revealed many kinematic features of this event, the mechanism and rupture dynamic characteristics underlying unexpectedly large surface dislocations need to be clarified. In this study, based on the grid search method, we conducted 61 dynamic rupture simulations considering terrain relief to screen out a preferred dynamic model that fits the geodetic, seismic, and geological observations well. The results show that the average stress drop of the nucleation part is relatively high (11 MPa), which could provide high initial rupture energy and give this event a chance to develop into a large earthquake. However, the rupture propagating eastward is slowed and terminated by two consecutive fault bends of about 10° each, and the westward propagating one might concentrate at a shallow depth (< 3 km) on the south secondary fault after it jumps over the stepover. These results imply that the complex fault geometry (the fault bend and stepover) might terminate the rupture early so that the observed magnitude of this event (Mw 6.6) is smaller than the estimated magnitude (Mw 7.1–7.2) based on the surface offsets. Our study again shows that, due to advances in computational power and observations (coverage and quality), physics-based dynamic rupture simulations have entered an era where it is possible to fit the observed data well, which is vital for further understanding the mechanisms of earthquakes.

Co-seismic deformation and related hazards associated with the 2022 Mw 5.6 Cianjur earthquake in West Java, Indonesia: insights from combined seismological analysis, DInSAR, and geomorphological investigations

IntroductionOn November 21, 2022, a magnitude Mw 5.6 earthquake struck Cianjur Regency in the West Java Province of Indonesia. It was followed by at least 512 aftershocks that persisted from November to June 2023. This seismic event occurred in an area previously unrecognized as an active fault zone. The consequences of this earthquake in Cianjur were severe, leading to both loss of life and extensive structural damage. The substantial damage to buildings was likely a result of abrupt alterations in the local topography due to surface deformation effects.ObjectivesThis research endeavor aims to spatially determine the patterns of ground surface deformation and its relationship with local geomorphological setting due to earthquakes in Cianjur in 2022.MethodsIn this study we conduct seismological analysis of 45 seismic stations, statistical analysis of mainshock and aftershocks data, RADAR Sentinel-1 imagery and employed the DInSAR methodology. Field survey was also conducted to determine the geomorphological characteristics in the study area.ResultsThe outcomes disclosed that the deformation encompassed both subsidence and uplift. The results signify that there was subsidence deformation in the vicinity of Cianjur and its environs during the primary earthquake on November 21, 2022, with an average deformation value of approximately -5 cm. In contrast, the measured deformation during the aftershocks exhibited uplift deformation, with an average value of 10 cm. The examination of deformation patterns amid the 2022 Cianjur earthquake sequence detects elevated deformation values in the vicinity of Cugenang district, with an orientation running from northwest to southeast. The geomorphological investigation conducted indicates that the region of Cianjur encompasses a variety of landforms, such as volcanic, structural, fluvial, and denudational. These landforms exhibit distinct responses to seismic activities. Co-seismic hazards, such as landslides frequently occur as a consequence of seismic events in mountainous terrain.Main ConclusionsSpatio-temporal variation of ground deformation could arise from various causes, such as the number and distribution of aftershocks, stress redistribution, fault interactions, secondary effects, and local geological settings. The mainshocks release accumulated stress along a fault, resulting in particular types of deformation, whereas aftershocks may redistribute stress exhibiting on adjacent faults. Secondary effects triggered by aftershocks, coupled with local geological and geomorphological conditions, further contribute to the diverse patterns of ground deformation observed during seismic events. The results of the study revealed that ground deformation had the greatest impact on fluvial, volcanic, and denudational processes, resulting in notable subsidence and uplift in specific regions. The occurrence and magnitude of co-seismic landslides were triggered by both mainshock and aftershock events, which occurred on weathered geological materials. These effects were further amplified by the simultaneous presence of the rainy season.ImplicationsThe knowledge gained from this research can be applied to evaluate the impacts of earthquakes and to proactively reduce future risks.

Earthquake source impacts on the generation and propagation of seismic infrasound to the upper atmosphere

SUMMARY Earthquakes with moment magnitude (Mw) ranging from 6.5 to 7.0 have been observed to generate sufficiently strong acoustic waves (AWs) in the upper atmosphere. These AWs are detectable in Global Navigation Satellite System satellite signals-based total electron content (TEC) observations in the ionosphere at altitudes ∼250–300 km. However, the specific earthquake source parameters that influence the detectability and characteristics of AWs are not comprehensively understood. Here, we extend our approach of coupled earthquake-atmosphere dynamics modelling by combing dynamic rupture and seismic wave propagation simulations with 2-D and 3-D atmospheric numerical models, to investigate how the characteristics of earthquakes impact the generation and propagation of AWs. We developed a set of idealized dynamic rupture models varying faulting types and fault sizes, hypocentral depths and stress drops. We focus on earthquakes of Mw 6.0–6.5, which are considered the smallest detectable with TEC, and find that the resulting AWs undergo non-linear evolution and form acoustic shock N waves reaching thermosphere at ∼90–140 km. The results reveal that the magnitude of the earthquakes is not the sole or primary factor determining the amplitudes of AWs in the upper atmosphere. Instead, various earthquake source characteristics, including the direction of rupture propagation, the polarity of seismic wave imprints on the surface, earthquake mechanism, stress drop and radiated energy, significantly influence the amplitudes and periods of AWs. The simulation results are also compared with observed TEC fluctuations from AWs generated by the 2023 Mw 6.2 Suzu (Japan) earthquake, finding preliminary agreement in terms of model-predicted signal periods and amplitudes. Understanding these nuanced relationships between earthquake source parameters and AW characteristics is essential for refining our ability to detect and interpret AW signals in the ionosphere.

Intraslab seismicity migration simultaneously with an interface slow slip event along the Ecuadorian subduction zone

Slow slip events (SSEs) are transient slip episodes taking place along the plate interface of subduction zones. They usually occur synchronously to tectonic tremors and/or seismic swarms, but the relationship between slip and seismicity remains unclear. Here, we study a well-instrumented seismic swarm-SSE sequence near a highly coupled segment along the Ecuadorian subduction zone. GPS data reveal that a one-week long SSE developed along the subduction interface at shallow depth (5–15 km) with an equivalent moment magnitude (Mw) of 6.3. During that period, a local temporary seismic network recorded >700 earthquakes with magnitudes ranging between 1.0 and 4.6. The distribution of seismicity illuminates a steep intraslab fault downdip of an oceanic relief, striking almost parallel to the trench. This seismicity migrates along strike of this active structure at a velocity of 10–15 km/day. This velocity is commonly observed in the case of slow slip propagation. Our observation suggests that the interplate SSE might have triggered a slow slip along the the intraslab active structure, which in turn drove the intraslab seismicity. In addition, at the northern part of the intraslab faults, a cluster of seismicity shows a radial expansion compatible with a fluid diffusion process. Overall, our study highlights the dynamical interaction between an interplate slow slip and an intraslab seismic swarm with the interplay of an intraslab aseismic slip propagation and fluid diffusion, both controlling the migration of seismicity.

Present-day quantification of seismic coupling along the décollement level beneath the Potwar Plateau region in Pakistan western Himalaya

Using GNSS horizontal surface velocities and Sentinel-1 interferometry line-of-sight velocities, we quantify the current velocity field of the Potwar Plateau Salt Range fold-and-thrust belt. From this velocity field indicating a creep of the Potwar Plateau along the Main Himalayan Thrust, we inferred a weak subhorizontal décollement level formed by a massive Precambrian salt layer. To the south of the Plateau, the Salt Range is uplifted along the Salt Range Thrust, conditioned by the presence of an inherited normal fault. The Kalabagh Fault, which forms the western boundary of the Salt Range and Potwar Plateau, exhibits a creep rate of 3.3 mm/yr. Numerical modelling enabled us to characterise the slip distribution and coupling along the faults, showing the presence of a large asperity along the décollement level beneath the Potwar Plateau and several asperities along the eastern part of this basal thrust. The model also indicated an alternation of coupled and decoupled zones along the Kalabagh Fault, suggesting that this strike-slip fault can be characterised by creep and the occurrence of earthquakes and/or slow slip events. Considering the lack of instrumental and historical large-magnitude earthquakes in this area, the Main Himalayan Thrust and Kalabagh Fault are likely to be affected by earthquakes of magnitude Mw larger than 7.5. A slip rate of 20 mm/yr is modelled along the southern and superficial parts of the Salt Range Thrust, which is larger than the 14 mm/yr slip rate along the Main Himalayan Thrust at depth. This observation suggests the existence of a southward flow of massive salt along the Salt Range Thrust.

February 6, 2023, Kahramanmaraş twin earthquakes: Evaluation of ground motions and seismic performance of buildings for Elazığ, southeast of Türkiye

On February 6, 2023, two strong earthquakes, magnitude (Mw) 7.7 and 7.6, occurred 9 h apart on the East Anatolian Fault Zone in Türkiye. These devastating earthquakes directly affected a region of southeastern Türkiye, where approximately 15 million people live and caused severe destruction of structures. Unfortunately, more than 50.000 people lost their lives as a result. The study presented the tectonic structure of Elazığ, one of the provinces affected by these earthquakes, in detail. Then, the general seismic characteristics of the main shock.Additionally, the geological structure, existing building stock, and seismicity of Elazığ province are given. Furthermore, the damages, deficiencies, misapplications and defects, and lack of engineering services and supervision seen in the building stocks due to the field investigation are presented and discussed in detail. Finally, some suggestions were made to prevent all these damages, to observe deficiencies/misapplications, and to take precautions for existing damaged buildings.

Offshore Fault Geometry Revealed from Earthquake Locations Using New State-of-Art Techniques: The Case of the 2022 Adriatic Sea Earthquake Sequence

Abstract Precise hypocenter locations are critical for properly interpreting earthquake occurrence processes. However, when the coverage with seismic stations is unfavorable or sparse, locating precisely earthquake hypocenters, in particular their depth, is challenging. Here we apply a newly developed approach, which uses only two land stations, to the recently occurred 2022 Adriatic Sea offshore earthquake sequence (mainshock of magnitude Mw 5.5) and achieve location results that are comparable to the catalog locations obtained using dozens of stations. First, six events with magnitudes M ≥3.0 were relocated using a travel-time stacking method. Next, using these six earthquakes as reference events, we applied a two-station differential travel-time method to reconstruct the earthquake cluster geometry and locate the remaining events, including the mainshock. The obtained earthquake distribution shows a dipping direction that varies from south to southwest, depending on the choice of the input parameters. Our preferred result shows a cluster dipping at an angle of ∼30° toward the south-southwest. This solution was chosen because the depth of the mainshock hypocenter obtained using the differential-time procedure agrees well with the depth constrained using depth phases. Moreover, the relatively sharp earthquake cluster geometry is in general consistent with the thrust fault structures revealed by a local seismic reflection survey and focal mechanism solutions.

Possible Interrelations of Space Weather and Seismic Activity: An Implication for Earthquake Forecast

The statistical analysis of the impact of the top 50 X-class solar flares (1997–2024) on global seismic activity as well as on the earthquake preparation zones located in the illuminated part of the globe and in an area of 5000 km around the subsolar point was carried out. It is shown by a method of epoch superposition that for all cases, an increase in seismicity is observed, especially in the region around the subsolar point (up to 33%) during the 10 days after the solar flare in comparison with the preceding 10 days. The case study of the aftershock sequence of a strong Mw = 9.1 earthquake (Sumatra–Andaman Islands, 26 December 2004) after the solar flare of X10.16 class (20 January 2005) demonstrated that the number of aftershocks with a magnitude of Mw ≥ 2.5 increases more than 17 times after the solar flare with a delay of 7–8 days. For the case of the Darfield earthquake (Mw = 7.1, 3 September 2010, New Zealand), it was shown that X-class solar flares and M probably triggered two strong aftershocks (Mw = 6.1 and Mw = 5.9) with the same delay of 6 days on the Port Hills fault, which is the most sensitive to external electromagnetic impact from the point of view of the fault electrical conductivity and orientation. Based on the obtained results, the possible application of natural electromagnetic triggering of earthquakes is discussed for the earthquake forecast using confidently recorded strong external electromagnetic triggering impacts on the specific earthquake preparation zones, as well as ionospheric perturbations due to aerosol emission from the earthquake sources recorded by satellites.

Analysis of the Fractal Dimension, b-value, Slip Ratio, and Decay Rate of Aftershock Seismicity Following the 6 February 2023 (Mw 7.8 and 7.5) Türkiye Earthquakes

On 6 February 2023, Türkiye experienced a pair of consecutive earthquakes with magnitudes of Mw 7.8 and 7.5, and accompanied by an intense aftershock sequence. These seismic events were particularly impactful on the segments of the East Anatolian Fault Zone (EAFZ), causing extensive damage to both human life and urban centers in Türkiye and Syria. This study explores the analysis of a dataset spanning almost one year following the Turkiye mainshocks, including 471 events with a magnitude of completeness (Mc) ≥ 4.4. We employed the maximum likelihood approach to estimate the b-value and Omori-Utsu parameters (K, c, and p-values). The estimated b-value is 1.21 ± 0.1, indicating that the mainshocks occurred in a region characterized by elevated stress levels, leading to a sequence of aftershocks of larger magnitudes due to notable irregularities in the rupture zone. The aftershock decay rate (p-value = 1.1 ± 0.04) indicates a rapid decrease in stress levels following the main shocks. However, the c-value of 0.204 ± 0.058 would indicate a relatively moderate or low initial productivity of aftershocks. Furthermore, the k-value of 76.75 ± 8.84 suggests that the decay of aftershock activity commenced within a range of approximately 68 to 86 days following the mainshocks. The fractal dimension (Dc) was assessed using the correlation integral method, yielding a value of 0.99 ± 0.03. This implies a tendency toward clustering in the aftershock seismicity and a linear configuration of the epicenters. The slip ratio during the aftershock activity was determined to be 0.75, signifying that 75% of the total slip occurred in the primary rupture, with the remaining fraction distributed among secondary faults. The methodologies and insights acquired in this research can be extended to assist in forecasting aftershock occurrences for future earthquakes, thus offering crucial data for future risk assessment.

Seismic characterisation of the subsoil under a historic building: Cathedral Church of Saint Mary in Murcia case study

This research focuses on the Cathedral Church of Saint Mary in Murcia, Spain, which is located in a moderate-to-high seismic risk zone in the Spanish context. The study uses geophysical techniques and geotechnical investigation to characterise seismic ground models at the building's scale, aiming to understand the real amplification of the ground under seismic effect in historic buildings. Three soil layers (silt, sand with gravel, and gravel) were identified through core borings. Multichannel Analysis of Surface Waves (MASW) profiles and Mini-array profiles revealed Vs values of 305 ± 32 m/s, 296 ± 62 m/s, and 440 ± 38.5 m/s, respectively, for these materials. Seismic Refraction Tomography (SRT) showed Vp values of 586 ± 73 m/s, 700 m/s, and 1466 ± 489 m/s for the corresponding layers. The horizontal-to-vertical spectral ratio (HVSR) approach identified a ground predominant period ranging from 0.37 to 0.38 s. Another significant peak at 2.3 s is observed, probably associated to the Triassic basement. Three seismic events with magnitudes Mw between 4.9 and 5.1 were used as inputs to determine the amplification factor (AF). The results indicate a PGA amplification factor between 1.7 and 2.1. These results contribute to the conservation and mitigation of seismic risk of this cultural heritage generating input data that enables precise computation of the soil-structure interaction.

Magnitudes and surface rupture lengths of paleo-earthquakes at the NW-part of the Peel Boundary fault zone, Roer Valley Rift System

The Peel Boundary Fault zone (PBFZ) is the 125 km long, seismically active, northern bounding fault zone of the Roer Valley Rift System (RVRS). The last damaging earthquake along the PBFZ was the Roermond earthquake of 1992. It had a magnitude of Mw 5.3 and no surface rupture. Previous results from two trenching studies located in the central and southeastern parts of the PBFZ provided evidence for two surface rupturing paleo-earthquakes. The largest earthquake had an estimated magnitude of Mw ∼6.8 and a surface rupture length of at least 35 km. As it took place around the Late Pleniglacial – Late Glacial transition a link to glacio-isostatic motions is likely. Results from a new trench situated at the northwestern part of the PBFZ shows evidence for three to four paleo-earthquakes, of which three were surface rupturing. These comprise two normal faulting- and one, younger trans-tensional displacement. The normal faulting events have ∼1 m vertical displacements each, which translate into magnitudes of Mw ∼7. Like the previous results, they occurred during the Late Pleniglacial-Late Glacial transition, at ∼15 ka and ∼ 14 ka. The younger trans-tensional event occurred sometime during the Holocene, pre-dating an unaffected, 13th century man-made paleo-channel on the hangingwall. The potential fourth, non-surface rupturing earthquake is indirectly evidenced by loading deformations of a sand layer and a collapsed brick-wall in the infill of the paleo-channel. Comparison of our trenching results to those from the two previous studies, which were located farther to the southeast along the PBFZ, shows that for one event a correlation is possible. The correlation would indicate a surface rupture length of at least 55 km. Combined, all trenching results indicate that the characteristic maximum rupturing displacement is ∼1 m, and thus that Mw ∼7 is the maximum magnitude of paleo-earthquakes along the PBFZ.

REHABILITATION APPROACH AFTER EARTHQUAKE DISASTER: A BRIEF REPORT FROM TURKEY.

Devastating earthquake disasters are experienced all over the world. On February 6, 2023, two major earthquakes with magnitudes of Mw 7.7 and 7.6, respectively, occurred centered in Kahramanmaraş, Turkey. It resulted in at least 50,783 deaths and more than 122,000 injuries according to official data. Defining the post-earthquake experiences and earthquake risk assessment well and identifying the deficiencies will guide the coordination, management, and planning of subsequent disasters. In this study, the rehabilitation approaches of earthquake victims with physical injuries in our rehabilitation center are emphasized and the situations that will be encountered in the immediate, intermediate, and long-term periods after the earthquake are summarized.

Seismic hazard analysis using Deterministic Seismic Hazard Analysis (DSHA) Method: A case study in Southern Malang District, East Java

Indonesia is a country that has a high earthquake threat. The United States Geological Survey (USGS) recorded that Indonesia experienced 5,439 earthquakes with a magnitude of Mw 5. Geologically, Indonesia is located about 200 km from the subduction zone of the Indo-Australian and Eurasian plates. Malang Regency faces the subduction of the Indo-Australian and Eurasian plates. Earthquakes that occur in plate subduction areas will propagate in various directions, including to Malang Regency. Thus, Malang Regency, especially in the southern part, has a high earthquake threat. This study aims to calculate the earthquake threat using a deterministic approach. Earthquake threats can be calculated using the Deterministic Seismic Hazard Analysis (DSHA) method. This study obtained the Mc. Guirre and Donovan attenuation function. These two attenuation functions produce different Peak Ground Acceleration values. The calculations with the Mc. Guirre attenuation function has a range of PGA values from 38,76461 gals to 69,78215 gals. Meanwhile, the Donovan attenuation function calculation produces a range of PGA values from 41.97550 gals to 76.21376 gals. Based on the value of ground acceleration during an earthquake, Bantur, Gedangan, and Sumbermanjing sub-districts are the sub-districts with the highest earthquake threat level in Southern Malang Regency. Tirtoyudo Village, Tirtoyudo District, Malang District has a lower PGA value when compared to Gedangan District. However, the amount of damage to buildings in this subdistrict was much higher. Since the building structure in Tirtoyudo Village cannot withstand ground shaking due to the earthquake, there is damage to the structure of the building.

Damage assessment of Siverek Castle during the Kahramanmaraş Earthquakes (Mw 7.7 and Mw 7.6) on 06 February 2023: Remediation and strengthening proposals

On February 6, 2023, two significant earthquakes with magnitudes (Mw) of 7.7 and 7.6 struck Turkey, occurring nine hours apart. In addition to the tragic loss of over 50,000 lives in the earthquakes centered in Kahramanmaraş, hundreds of thousands of engineering structures, such as residences, schools, hospitals, historical landmarks, highways, and more, were severely damaged. This study assesses the damages and risk scenario following the Kahramanmaraş earthquakes concerning Siverek Castle. In addition, remediation and strengthening proposals, required to eliminate the damage and the possible risk, have been developed. The initial stage involved observational damage assessments on the castle and surrounding slopes as part of field studies, identifying five different types of damage and potential risks. Subsequently, a precise 3D digital model of the damaged castle and its slopes was generated using the digital photogrammetry method. Additionally, geological and geophysical studies were conducted in the field to determine the characteristics of the mound structure, historical castle walls, soil and rock on the slope. Non-destructive, geophysical methods consisting Vertical Electrical Sounding (VES), Seismic Refraction Method (SRM) and Multichannel Analysis of Surface Waves (MASW) measurements were specifically employed in the area with historical remnants. To verify the obtained data, five boreholes were drilled in the lower parts of the slope, and experimental studies were conducted to determine the soil and rock material properties of the slope. In the numerical studies, a total of 54 2D stability analyses were performed under static, long-term static, and dynamic conditions. Additionally, 1000 different probabilistic rockfall analyses were conducted, both in 2D and 3D, to calculate the run-out distance, bounce height, velocity, and kinetic energies of the blocks that fell or were about to fall during the earthquake. In the final stage of the study, remediation and strengthening recommendations were prepared for the strengthening of the fortification walls and slopes where failures occurred, and stability analyses were conducted. Consequently, a design proposal recommending five distinct approaches to remediate and strengthen the castle and slopes impacted by the Kahramanmaraş earthquakes was endorsed by the relevant authorities, and construction has commenced. When the remediation and strengthening works are completed, the security of the cultural heritage will be ensured, and it is planned to be opened to visitors.