The spatiotemporal pattern of surface displacements from large earthquakes provides crucial insights about the deformation of Earth’s crust at various scales and the interactions among tectonic plates. However, the lack of extensive and large-scale geodetic networks near such seismic events hinders our thorough understanding of the large-scale crustal deformation resulting from earthquakes. Using Türkiye’s extensive and continuous global navigation satellite system (GNSS) network during the moment magnitude 7.8 and 7.6 Kahramanmaraş earthquakes on 6 February 2023, we show that large earthquakes can induce far-field crustal deformations (>700 kilometers), exceeding current predictions from elastic dislocation models. They can lead to the mobilization of tectonic plates and the triggering of far-field earthquakes, which carries profound implications for seismic hazard assessments and necessitates a new perspective on crustal deformation and earthquake mechanics.

The Global Navigation Satellite System (GNSS) signal experiences delays caused by the atmosphere, leading to the lengthening of the geometric path of the ray, commonly referred to as tropospheric delay. This delay is a significant source of error in GNSS positioning, contributing to a bias in the height component of several centimeters, even when meteorological data are simultaneously recorded and used in tropospheric models. In this study, considering seasonal variations, we investigated the impact of tropospheric delay on the GNSS height component. GNSS stations, part of the Turkish RTK CORS Network known as TUSAGA-Active (Turkish National Permanent GNSS Network Active), covered different heights over the 2014–2019 period. Daily coordinates of GNSS stations and tropospheric zenith delay were obtained through the GAMIT/GLOBK software solution.In the study, temperature, pressure, and relative humidity data of meteorological stations at different heights were converted to mean sea level. By using these values, interpolation estimates were made for the continuous GNSS stations in the same region with the IDW method. The most significant delay in GNSS signals occurs in July and August. This effect, which causes periodic changes in the zenith delay, varies inversely with the station's height. With the increase in the amount of water vapor in the atmosphere in parallel with the rise in the temperature in the summer months, it is seen that the stations at a low height are more exposed to the tropospheric effect than the stations at higher heights. In addition, GNSS stations' reduced meteorological values (temperature, pressure and relative humidity) show that the zenith delay values changed directly proportional to the temperature and inversely proportional to the pressure and relative humidity.

Slow, aseismic slip plays a crucial role in the initiation, propagation, and arrest of large earthquakes along active faults. In addition, aseismic slip controls the budget of elastic strain in the crust, hence the amount of energy available for upcoming earthquakes. The conditions for slow slip include specific material properties of the fault zone, pore fluid pressure, and geometrical complexities of the fault plane. Fine scale descriptions of aseismic slip at the surface and at depth are key to determine the factors controlling the occurrence of slow, aseismic versus rapid, seismic fault slip. We focus on the spatial and temporal distribution of aseismic slip along the North Anatolian Fault, the plate boundary accommodating the 2 cm/yr of relative motion between Anatolia and Eurasia. Along the eastern termination of the rupture trace of the 1944 M7.3 Bolu-Gerede earthquake lies a segment that slips aseismically since at least the 1950s. We use Sentinel 1 time series of displacement and GNSS data to provide a spatio-temporal description of the kinematics of fault slip. We show that aseismic slip observed at the surface is coincident with a shallow locking depth and that slow slip events with a return period of 2.5 years are restricted to a specific section of the fault. In the light of historical measurements, we discuss potential rheological implications of our results and propose a simple alternative model to explain the local occurrence of shallow aseismic slip at this location.

This study aims to determine the datum definition for the geodetic vertical velocity field derived from temporary and continuous GNSS observations. The observations have been analysed to investigate how the effect of vertical velocity for GNSS stations depends on the reference station selection. For this purpose, a network consisting of 26 GNSS stations has been designed. The GNSS observations have been processed using Bernese GNSS software v5.2 according to the different strategies. The strategies have been generated from ten different datum definitions of one to ten continuous GNSS stations within the IGS network in the Eurasia region, which is thought to be the least affected by tectonic movements. The vertical velocities of our solution derived from four reference stations concur within 0.4 mm/yr with those of the IGS/EUREF/NGL solution. It has been determined that the vertical velocities obtained based on the four reference stations proposed within the scope of the study are equal to the vertical velocities obtained from the ten stations distributed over the European region. The usability of these outcomes has been investigated in the studies to be carried out on Turkey's west and south coasts.

The paper presents the velocity field of the Western Caucasus and Ciscaucasia based on GNSS observations. In the ITRF2014 reference frame, this field shows the coordinated movement of the region in the north‒northeast direction at an average rate of 27‒28 mm/year. A number of geodynamic features of the main tectonic structures of the region are identified with respect to fixed (immobile) Eurasia. In the northern part of the region, a fan-shaped pattern of horizontal velocity vectors is observed, reflecting counterclockwise rotation of the northern limb of the North Azov flexural fault zone and, accordingly, modern shear displacements. To detail the geodynamic situation, the velocity field is compared with two geodetic profiles. The first profile crosses in the southwest–northeast direction the mountain belt of the Western Caucasus, the West Kuban Foredeep, and the Scythian Platform, which are the region’s main geological structures. The second profile is less extended, but also crosses the entire mountain belt of the Western Caucasus, the West Kuban Foredeep, and part of the monocline of the Central Sector of the North Caucasus. Within the Greater Caucasus and the West Kuban Foredeep, transverse compression of the main morphostructures is observed at a rate of up to 1 mm/year, and shear displacements prevail in the Ciscaucasia. The mountain belt of the Western Caucasus is in conditions of longitudinal compression. East of the Tuapse Fault Zone, the mountain belt is undergoing longitudinal extension. At the same time, the intensity of deformation processes on the southern slope area is higher than in the Ciscaucasia. Currently, the seismic activity level in the Western Caucasus is low and moderate.

Abstract. Earthquake-induced submarine slope destabilization is known to cause debris flows and turbidity currents, but the hydrodynamic processes associated with these events remain poorly understood. Records are scarce and this notably limits our ability to interpret marine paleoseismological sedimentary records. An instrumented frame comprising a pressure recorder and a Doppler recording current meter deployed at the seafloor in the Sea of Marmara Central Basin recorded consequences of a MW = 5.8 earthquake occurring Sept 26, 2019 and of a Mw = 4.7 foreshock two days before. The smaller event caused sediment resuspension but no strong current. The larger event triggered a complex response involving a mud flow and turbidity currents with variable velocities and orientations, which may result from multiple slope failures. A long delay of 10 hours is observed between the earthquake and the passing of the strongest turbidity current. The distance travelled by the sediment particles during the event is estimated to several kilometres, which could account for a local deposit on a sediment fan at the outlet of a canyon, but not for the covering of the whole basin floor. We show that after a moderate earthquake, delayed turbidity current initiation may occur, possibly by ignition of a cloud of resuspended sediment. Some caution is thus required when tying seismoturbidites with earthquakes of historical importance. However, the horizontal extent of the deposits should remain indicative of the size of the earthquake.

GNSS networks play an important role in monitoring the displacements, movements and deformations of the Earth's crust and engineering buildings. In this study, we examine how GPS Precise Point Positioning (PPP) is able to determine the horizontal deformations with respect to the GPS network solution. For this purpose, 7 days data of 12 Continuously Operating Reference Stations (CORS) in Turkey (CORS-TR), located in the western part of Turkey, are considered. The Bernese (v5.2)-derived coordinates over 7 days and the ones from four free online PPP services (CSRS, GAPS, APPS, Magic-PPP) are compared using the Bursa-Wolf coordinate transformation model. The errors from these transformations are used to define the RMS values of the PPP solutions in the local coordinate system. These values are relative to the GPS network solution. This fact leads to analysing how the PPP solutions are able to determine the horizontal deformations with respect to the network solution. From many experiments, in which the displacements belonging to the PPP solutions are simulated relative to the network solution, it has been shown that several ppm extensions or contractions may be determined using the free online PPP services. Therefore, we conclude that the online PPP services studied here may be used in 2D deformation studies as an alternative to the GPS network solutions.

During the past century, a series of predominantly westward migrating M>7 earthquakes broke an similar to 1000km section of the North Anatolian Fault (NAF). The only major remaining seismic gap along the fault is under the Sea of Marmara (Main Marmara Fault (MMF)). We use 20years of GPS observations to estimate strain accumulation on fault segments in the Marmara Sea seismic gap. We report the first direct observations of strain accumulation on the Princes' Islands segment of the MMF, constraining the slip deficit rate to 10-15mm/yr. In contrast, the central segment of the MMF that was thought to be the most likely location for the anticipated gap-filling earthquakes shows no evidence of strain accumulation, suggesting that fault motion is accommodated by fault creep. We conclude that the Princes' Islands segment is most likely to generate the next M>7 earthquake along the Sea of Marmara segment of the NAF.

This paper reports on the estimation of changes of a GPS-based crustal deformation field as function of the observing session duration. This investigation was carried out on the Marmara Continuous GPS Network (Marmara region) by using UPS data collected on a set of 10 stations during the period 2002.50-2005.47 The GPS observations were processed in the ITRF 2005 reference frame using Bernese v5.0 software.Main results indicate that GPS data observation periods of 24 h are significantly more accurate than estimates determined from the short observing session. The squared sum of residuals for the 4-h data set (between 12:00 and 16:00 local time) are larger than the other data sets, probably due to the higher ionospheric effects during this time. Also, the deformation pattern obtained from the results of 8 h or more of the GPS data observations as depends on baseline length approaches to the deformation obtained from the results of 24 h GPS data observations. (C) 2013 COSPAR. Published by Elsevier Ltd. All rights reserved.

The aim of this study is to investigate the accuracy of GPS (Global Positioning System) positioning determined by GPS measurements carried out during the seasonal variations. The observations have been analyzed to determine how the accuracy of derived relative positions of GPS stations depends on the baseline length, the duration of observing session and the seasonal variations.For this purpose, we selected three days of each month in 2009 from the GPS observations made in the Marmara Continuous GPS Network (MAGNET). The GPS observations were processed in the ITRF 2005 reference frame using the Bernese 5.0 GPS software. The baseline length varies between 6 km and 237 km, session duration varies between 4 h and 24 h. Seasonal variation effects on the accuracy of coordinate components were analyzed. Our results showed that seasonal variation is a significant factor for determining the accuracy of GPS measurements. Also, increasing the observation period hardly improves the horizontal positioning accuracy while improving the vertical positioning accuracy. (C) 2014 Elsevier Ltd. All rights reserved.

We described the first results of an on-going study of absolute gravity changes after the 17 August 1999 Izmit earthquake in Marmara region. Repeated absolute gravity measurements were carried out six stations with an A10 absolute gravimeter from 2009 to 2011 in the region. A gravimetric calibration baseline (of the range of about 415 milliGal (mGal), 1 mGal=10−5 ms−2) was established in the region for the purposes of the calibration of the relative gravimeters. The absolute gravity measurements, repeated twice a year (October, June), can resolve gravity changes with a precision better than 5 microGal (μGal)/yr interval.

In this paper, we aim to determine a snapshot of previously unstudied ionospheric variations which were recorded in a two-week interval before and after a large earthquake of M 7.6 occurred on 17 August, 1999, in the Marmara region of Turkey. We detected ionospheric perturbations before the earthquake occurred using Global Positioning System (GPS) data received from the Marmara Continuous GPS Network (MAGNET). Pre-seismic ionospheric total electron content (TEC) anomalies were observed three days before the earthquake at sets of stations near the earthquake location, while post-seismic traveling ionospheric disturbances could not be detected. The ionospheric variability had a negative sign with an enhancement of about 8–10 TECU (1 TECU = 1016 electrons/m2) relative to the non-distributed state of the ionosphere. The results show that this method will be a useful addition to the already-available continuous monitoring techniques in the region.

Gravimetry has the potential to provide important data, in combination with GPS, for detecting vertical surface motions and subsurface mass changes. Here, we focus on the first results of joint gravity and GPS studies in order to understand better the vertical component of the postseismic deformations of the 1999 earthquakes along the western North Anatolian Fault. We investigate the relationship between gravity changes and GPS motions during the period 2003–2005. The changes in this period constitute a snapshot of the nonlinear movements that were not studied before in the Marmara Region. The first observations evaluated here demonstrate that the joint analysis of GPS and gravity data help to constrain the 3D postseismic deformations and hence expand our knowledge of the geophysical process in the Marmara Region. We identify what appear to be different crustal properties in the western and eastern parts of the region. Furthermore, the GPS results indicate that the western extension of the 1999 İzmit rupture area presently has low strain accumulation. To the extent that this behaviour continues through the earthquake cycle, it reduces the moment release of the expected future earthquake in the eastern Marmara seismic gap. In contrast, the western part of Marmara region has important strain loading. While our results are not sufficiently accurate for detailed interpretation, the observed strain accumulation implies the potential for a significant earthquake in the western Marmara region. Generally, possible fault creep extending west of the İzmit fault break following the İzmit earthquake is very important to understand the future seismic hazard in the Marmara region because it reduces the amount of strain accumulation during the earthquake cycle which will either delay the onset of future events or produce smaller future earthquakes.

The accuracy of GPS (Global Positioning System) derived relative positions of stations depends on several factors. Besides the baseline length and duration of observation session, the methodology and the software used influence the results. In this paper, the observations made in the Marmara Continuous GPS Network (MAGNET) have been analysed to determine how the accuracy of derived relative Positions of GPS stations depends on the baseline length and the duration of the observing session. Seven days of GPS observations in the MAGNET collected in 2002 were processed in the ITRF 2000 reference frame using Bernese 4.2 software. The baseline length varies between 6 km and 340 km, the session duration varies between 4h and 24h. The independent baseline components have been analysed.