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A strong motion seismometer is a kind of inertial sensor, and it can record middle- to high-frequency ground accelerations. The double-integration from acceleration to displacement amplifies errors caused by tilt, rotation, hysteresis, non-linear instrument response, and noise. This leads to long-period, non-physical baseline drifts in the integrated displacements. GNSS enables the direct observation of the ground displacements, with an accuracy of several millimeters to centimeters and a sample rate of 1 Hz to 50 Hz. Combining GNSS and a strong motion seismometer, one can obtain an accurate displacement series. Typically, a Kalman filter is adopted to integrate GNSS displacements and strong motion accelerations, using the empirical values of noise uncertainty. Considering that there are significantly different errors introduced by the above-mentioned tilt, rotation, hysteresis, and non-linear instrument response at different stations or at different times at the same station, it is inappropriate to employ a fixed noise uncertainty for strong motion accelerations. In this paper, we present a Sage–Husa Kalman filter, where the noise uncertainty of strong motion acceleration is adaptively estimated, to integrate GNSS and strong motion acceleration for obtaining the displacement series. The performance of the proposed method was validated by a shake table simulation experiment and the GNSS/strong motion co-located stations collected during the 2023 Mw 7.8 and Mw 7.6 earthquake doublet in southeast Turkey. The experimental results show that the proposed method enhances the adaptability to the variation of strong motion accelerometer noise level and improves the precision of integrated displacement series. The displacement derived from the proposed method was up to 28% more accurate than those from the Kalman filter in the shake table test, and the correlation coefficient with respect to the references arrived at 0.99. The application to the earthquake event shows that the proposed method can capture seismic waveforms at a promotion of 46% and 23% in the horizontal and vertical directions, respectively, compared with the results of the Kalman filter. [ABSTRACT FROM AUTHOR]

Large earthquakes can trigger smaller seismic events, even at significant distances. The process of earthquake triggering offers valuable insights into the evolution of local stress states, deepening our understanding of the mechanisms of earthquake nucleation. However, our ability to detect these triggered events is limited by the quality and spatial density of local seismometers, posing significant challenges if the triggered event is hidden in the signal of a nearby larger earthquake. Distributed acoustic sensing (DAS) has the potential to enhance the monitoring capability of triggered earthquakes through its high spatial sampling and large spatial coverage. Here, we report on an uncatalogued magnitude (M) 5.1 event in northeast Turkey, which was likely dynamically and instantaneously triggered by the 2023 M7.8 earthquake in southeast Turkey, located 400 km away. This event was initially discovered on ∼1,100 km of active DAS recordings that are part of an 1,850‐km linear array. Subsequent validation using local seismometers confirmed the event's precise time, location, and magnitude. Interestingly, this dynamically triggered event exhibited precursory signals preceding its P arrivals on the nearby seismometers. It can be interpreted as the signal from other nearby, uncatalogued, smaller triggered events. Our results highlight the potential of high‐spatial‐density DAS in enhancing the local‐scale detection and the detailed analysis of earthquake triggering. Plain Language Summary: Large earthquakes can trigger smaller ones even far away. This helps us understand more about how earthquakes start and develop. However, finding these smaller earthquakes can be difficult as sometimes they are hidden in the chaos of a bigger, nearby earthquake. There is a novel technology called Distributed Acoustic Sensing (DAS) that might help. DAS can listen for earthquakes over large areas and gives a more detailed picture of what's happening underground. In this study, we discovered a moderate‐size earthquake with a magnitude of 5.1 in Northeast Turkey that was triggered by a large earthquake with a magnitude of 7.8 in Southeast Turkey, using a DAS system that stretched over a thousand kilometers. We then checked this finding with conventional seismometers to be sure. Interestingly, this triggered earthquake showed precursory signals before its main shaking started, which could be signs of other smaller earthquakes happening nearby. Our findings deepen our understanding of how earthquakes interact with each other and offer insights into how earthquakes start. Our results also suggest that DAS could help us find and understand these triggered earthquakes, providing us with invaluable information for future seismology studies. Key Points: We find an uncatalogued M5.1 earthquake in NE Turkey dynamically and instantaneously triggered by the 2023 Mw 7.8 SE Turkey earthquakeWe uncover this event on a thousand‐kilometer linear distributed acoustic sensing array, then confirm its precise time, location, and magnitude with seismometersPrecursory signals of the M5.1 event are observed and are most likely resulting from other nearby events rather than its nucleation phase [ABSTRACT FROM AUTHOR]

On February 6, 2023, at 01 : 17 UTC, a M = 7.8 earthquake struck the southern area of Turkey near Gaziantep town and was followed by a second earthquake of M = 7.5 at 10 : 24 UTC with the epicenter in Elbistan city. Both events were associated with the Anatolian Fault System and have claimed over 50,000 victims, as reported by the Disaster and Emergency Management Authority, and caused serious damage in the regions of southern Turkey and northern Syria. Seismic waves related to strong Turkey earthquakes have been recorded both by seismic stations throughout the globe and on other devices such as the ground deformation (GNSS, strainmeters, or tiltmeters) networks. In this paper, we show and analyze the earthquake signals recorded by bore-hole tilt stations that monitor seismic and volcanic activities at Mt. Etna. Tilt stations showed very large variations, despite their distance from the epicenter (approximately 1950 km) with a period between 10 and 25 seconds. We compared tilt and seismic data for a co–located station evidencing a very similar waveform that highlight how tiltmeters respond to translational acceleration rather than ground tilt during a teleseism, suggesting that, for waves with this period, they may behave as horizontal seismometers. By using these signals, we evidence the different behaviors of two of the most used models of tiltmeters on volcanoes (Lily and Pinnacle) and how they are useful for instrument calibration. [ABSTRACT FROM AUTHOR]

This study includes the properties and installation stages of the microseismic network planned to be installed in a geothermal field in Turkey, which is currently producing electricity, in order to monitor the induced seismicity that will occur due to production and re-injection wells. The results of how the optimum microseismic monitoring network should be installed, the installation studies and the noise analysis of the station locations are given for this and similar geothermal fields. 7 borehole type seismometers were placed in wells drilled 65 meters deep and microseismic records of the field were obtained. The leading field equipment is SARA-SS10BHV three-component (3C) borehole type short-period velocity seismometers, and the analog data were digitized with 24-bit SL06 brand recorders. In data analysis, high frequency, low energy and small amplitude microseismic events were dealt within passive seismic records. Therefore, noise analysis is the most important step of the network installation. In the noise analysis studies, the background noise at the locations where the microseismic network stations will be deployed was determined by measurements from both on the surface and through the well, and then the results were compared with each other. According to the results, it has been determined that the noise level in the well is very low compared to the surface and this is at a suitable level for microseismic monitoring networks. [ABSTRACT FROM AUTHOR]

Understanding the crustal structure of the Anatolian Plate has important implications for its formation and evolution, including the extent to which its high elevation is maintained isostatically. However, the numerous teleseismic receiver function studies from which Anatolian Moho depths have been obtained return results that differ by ≤21 km at some seismograph stations. To address this issue, we determine Moho depth and bulk crustal VP / VS ratio (κ) at 582 broad-band seismograph stations, including ∼100 for which H – κ results have not been reported previously. We use a modified H – κ stacking method in which a final solution is selected from a suite of up to 1000 repeat H – κ measurements, each calculated using randomly selected receiver functions and H – κ input parameters. Ten quality control criteria that variously assess the final numerical result, the receiver function data set, and the extent to which the results are clustered tightly, are used to determine station quality. By refining Moho depth constraints, including identifying 182 stations, analysed previously, where H – κ stacking yields unreliable results (particularly in Eastern Anatolia and the rapidly uplifting Taurides), our new crustal model (ANATOLIA-HK21) provides fresh insight into Anatolian crustal structure and topography. Changes in Moho depth within the Anatolian Plate occur on a shorter length-scale than has sometimes previously been assumed. For example, crustal thickness decreases abruptly from >40 km in the northern Kirsehir block to <32 km beneath the Central Anatolian Volcanic Province and Tuz Golu basin. Moho depth increases from 30–35 km on the Arabian Plate to 35–40 km across the East Anatolian Fault into Anatolia, in support of structural geological observations that Arabia–Anatolia crustal shortening was accommodated primarily on the Anatolian, not Arabian, Plate. However, there are no consistent changes in Moho depth across the North Anatolian Fault, whose development along the Intra-Pontide and İzmir-Ankara-Erzincan suture zones was more likely the result of contrasts in mantle lithospheric, not crustal, structure. While the crust thins from ∼45 km below the uplifted Eastern Anatolian Plateau to ∼25 km below lower-lying western Anatolia, Moho depth is generally correlated poorly with elevation. Residual topography calculations confirm the requirement for a mantle contribution to Anatolian Plateau uplift, with localized asthenospheric upwellings in response to slab break-off and/or lithospheric dripping/delamination example candidate driving mechanisms. [ABSTRACT FROM AUTHOR]

By using P and S wave receiver functions and P and S wave travel time residuals, we have found velocity models for 16 seismograph stations in Eastern Anatolia. Our study is focused mainly on the mantle lithosphere, asthenosphere and transition zone. The volcanism and uplift of the Eastern Anatolia Plateau are thought to be related to the Bitlis slab break off and delamination of the continental lithosphere. Sinking cold slab and lithospheric drips can reduce temperature in the mantle transition zone (MTZ) by up to a few hundred degrees C. However, our analysis of seismic data provides no robust evidence of significant cooling of the transition zone. In the mantle immediately above the 410-km discontinuity there is a pronounced low S wave velocity layer that may be a source of the volcanism in the study region. Another low velocity layer is present at the base of the MTZ. The obtained S wave velocity models of the upper mantle can be divided into three groups. In the first group, the lithosphere—asthenosphere boundary (LAB) is at a depth of ~ 60 km. In the second group, the LAB is at a depth from 90 to 100 km. In the third group, the mantle lithosphere is practically absent. On a scale of our analysis there is no clear correspondence between the obtained mantle velocity models and the volcanism (< 23 Ma) exposed at the surface. Only the models of the first group are well represented in the neighboring Central Anatolian Plateau. [ABSTRACT FROM AUTHOR]

This study presents the general features of the structural health monitoring (SHM) system of the long-span cable-supported bridges in Turkey, namely the First Bosphorus Bridge, the Second Bosphorus Bridge (Fatih Sultan Mehmet Bridge), the newly constructed the Third Bosphorus Bridge (Yavuz Sultan Selim) and the Osman Gazi Bridge (Izmit Bay Bridge). Due to the critical function of the bridges in the transportation networks of Istanbul, structural health under extreme and operational load cases without interruption of their operation is essential. The SHM systems are already available and in use for the First and Second Bosphorus Bridges; however, the Yavuz Sultan Selim and the Osman Gazi Bridges, only have the preliminary SHM systems established. General preferences of the current and planned SHM systems of the bridges are given based on the monitoring objectives and requirements. Data collected from the SHM systems are also exhibited as an illustration for structural modal identification of the First Bosphorus Bridge. Based on the experiences from the current SHM systems, future works and planning are recommended to effectively design new SHM system and to efficiently update the current ones. [ABSTRACT FROM AUTHOR]

The horizontal to vertical spectral ratios of microtremor (HVSR) analysis of Yüksekova and its surroundings is carried out using the results of field investigations, local soil conditions and seismotectonic features of the region. Soil-structure interaction is one of the most important reason for building damage ratio. The effects of soil conditions on probably damaged building units were determined, by conducting HVSR microtremor measurements. In this study data collection is handled during 30 min using three component seismograph measurements at 40 points in the Yüksekova region. HVSR peak period map shows that the fundamental period range between 0.4 and 1.6 s in the soft sediments units. Rock sites of the northern coast of Yüksekova period range between 0.1 and 0.2 s. HVSR peak amplitude values are in the interval 1.5–6.0. [ABSTRACT FROM AUTHOR]

The lateral variation of the stress field in the southern Aegean plate and the subducting Hellenic slab is determined from recordings of seismicity obtained with the CYCNET and EGELADOS networks in the years from 2002 to 2007. First motions from 7000 5 well-located earthquakes were analysed to produce 540 well-constrained focal mechanisms. They were complemented by another 140 derived by waveform matching of records from larger events. Most of these earthquakes fall into 16 distinct spatial clusters distributed over the southern Aegean region. For each cluster, a stress inversion could be carried out yielding consistent estimates of the stress field and its spatial varia10 tion. At crustal levels, the stress field is generally dominated by a steeply dipping compressional principal stress direction except in places where coupling of the subducting slab and overlying plate come into play. Tensional principal stresses are generally subhorizontal. Just behind the forearc, the crust is under arc-parallel tension whereas in the volcanic areas around Kos, Columbo and Astypalea tensional and intermedi15 ate stresses are nearly degenerate. Further west and north, in the Santorini-Amorgos graben and in the area of the islands of Mykonos, Andros and Tinos, tensional stresses are significant and point around the NW-SE direction. Very similar stress fields are observed in western Turkey with the tensional axis rotated to NNE-SSW. Intermediate depth earthquakes below 100 km in the Nisyros region indicate that the Hellenic slab 20 experiences slab-parallel tension at these depths. The direction of tension is close to east-west and thus deviates from the local NW-oriented slab dip presumably owing to the segmentation of the slab. Beneath the Cretan sea, at shallower levels, the slab is under NW-SE compression. The lateral and depth variations of the stress field reflect the various agents that influence tectonics in the Aegean: subduction of the Hellenic 25 slab, incipient collision with continental African lithosphere, roll back of the slab in the south-east, segmentation of the slab, arc volcanism and extension of the Aegean crust. [ABSTRACT FROM AUTHOR]

SUMMARY Different types of 4-component ocean bottom seismometers (OBS) were deployed for variable durations ranging from 1 week to about 4 months in 2007, over soft sediments covering the seafloor of the Tekirdag Basin (western part of the Sea of Marmara, Turkey). Non-seismic microevents were recorded by the geophones, but generally not by the hydrophones, except when the hydrophone is located less than a few tens of centimetres above the seafloor. The microevents are characterized by short durations of less than 0.8 s, by frequencies ranging between 4 and 30 Hz, and by highly variable amplitudes. In addition, no correlation between OBSs was observed, except for two OBSs, located 10 m apart. Interestingly, a swarm of ∼400 very similar microevents (based on principal component analysis) was recorded in less than one day by an OBS located in the close vicinity of an active, gas-prone fault cutting through the upper sedimentary layers. The presence of gas in superficial sediments, together with analogies with laboratory experiments, suggest that gas migration followed by the collapse of fluid-filled cavities or conduits could be the source of the observed microevents. This work shows that OBSs may provide valuable information to improve our understanding of natural degassing processes from the seafloor. [ABSTRACT FROM AUTHOR]

Abstract: We have used receiver function analysis employing teleseismic waveforms to investigate variations in crustal and upper-mantle velocity structure beneath the western Turkey. The genetic algorithm is adopted to avoid the inherent non-uniqueness problems of the inversion. The total of 50 teleseismic waveforms recorded by 25 permanent stations is analyzed and the selected records of earthquakes distributed in three quadrants from each seismic station in the years from 2007 to 2008 are analyzed. 2-D images of Moho variation beneath the western Turkey along two profiles are 700 and 300km long and extended from the Aegean Sea coast to the central Anatolia and southeastern Anatolia respectively are estimated. The depth-migrated receiver function showed almost well resolved Moho for the two profiles. Although the limited quantity of data is used to short periods, the resolution and confidence level is not so bad. For the one profile that extended from the Aegean Sea coast to central Anatolia, we obtain Moho depths between 25 and 35km. On the other profile along the western coast, the Moho depths range from 20 and 30km. Shear wave speed was found to vary between 3.3km/s and 3.7km/s in the lower crust, and between 4.1km/s and 4.4km/s uppermost mantle. We concluded that the Moho depth is increasing from western Anatolia to central Anatolia considering inversion results and 2-D depth-migrated receiver functions. [Copyright &y& Elsevier]

A moderate-size earthquake (Mw = 6.2) occurred on 3 February 2002 (07:11:28 GMT) in the Sultandağı-Çay region of southwest Turkey. The mainshock was followed by a strong aftershock of Mw = 6.0 just 2 h after the mainshock, at 09:26:49 GMT. A temporary seismic network of 27 vertical component seismometers was installed to monitor aftershock activity. One thousand sixty nine aftershocks (0.2 [ABSTRACT FROM AUTHOR]

Beneath the Marmara Sea, Turkey, the Main Marmara Fault (MMF), the offshore part of the North Anatolian Fault (NAF), is a well-known seismic gap for future M > 7 earthquakes. However, its detailed fault geometry and microearthquake activity have been debated for several decades. Using data acquired from long-term ocean bottom seismograph (OBS) observations, we made precise hypocenter estimations based on 3-D Vp and Vs velocity structures and assessed the fault geometry beneath the western and central parts of the MMF. The results indicate a segmentation boundary between the near-vertical western part and the south-dipping eastern part located around 28.10°E. Enriched OBS locations indicate microseismicity along both the inner and outer boundary faults of the Central Basin, especially on the western side. A comparison with previously published results suggests that the seismicity pattern has not changed for at least two years, between 2014 and 2016. Using a combined dataset of this and previous studies, lateral variations in the dip angle along the MMF fault segment from 27.4°E to 28.8°E were investigated. Based on this, we depicted on-fault seismicity along the MMF and defined three inactive areas of microseismicity. Two are located in the western segment, corresponding to the rupture area of the 1912 Ms. 7.4 earthquake, and the other, the largest, is located on the eastern segment. From a comparison of previous seismic and geodetic studies, it is considered that this area is a fully locked zone and has the potential for large earthquakes. Having compared the difference between hypocenter locations determined from OBSs and land-based stations, it is proposed that the epicentral locations of the mainshock and aftershocks of the September 26, 2019, M 5.7 earthquake are located much closer to the MMF than locations reported from only land-based results. • A segmentation boundary on the Main Marmara Fault is identified beneath the Central Basin. • Both inner and outer boundary faults of the Central Basin are developed in the western Central Basin. • Zones of no seismicity beneath the Kumburgaz Basin have the potential for a large earthquake. • The focal area of the September 2019 M 5.7 event was close to the Main Marmara Fault. [ABSTRACT FROM AUTHOR]