During the past century, a series of predominantly westward migrating M > 7 earthquakes broke an ~1000 km 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 20 years 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 10–15 mm/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.
Key Points
The first direct constraints on strain accumulation within the Sea of MarmaraPrinces' Islands segment likely represents the most imminent dangerThe central Marmara segment is not accumulating strain at significant rates
We have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 Izmit and Düzce earthquake ruptures, using a three‐dimensional viscoelastic finite element method. Our ...models confirm earlier findings that surface deformation within the first few months of the Izmit earthquake is principally due to stable frictional afterslip on and below the Izmit earthquake rupture. A second deformation process is required, however, to fit the surface deformation after several months. Viscoelastic relaxation of lower crust and/or upper mantle with a viscosity of the order of 2 to 5 × 1019 Pa s improves the models' fit to later GPS site velocities. However, for a linear viscous rheology, this range of values is inconsistent with highly localized interseismic deformation around the North Anatolian Fault Zone (NAFZ) that was well observed prior to the earthquake sequence. The simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes, that is, that it has a power law or Burger's body (transient) rheology. A Burger's body rheology with two characteristic viscosities (2 to 5 × 1019 Pa s and at least 2 × 1020 Pa s) in the mantle is consistent with deformation around the NAFZ throughout the earthquake cycle.
Abstract Short term prediction of earthquake magnitude, time, and location is currently not possible. In some cases, however, documented observations have been retrospectively considered as ...precursory. Here we present seismicity transients starting approx. 8 months before the 2023 M W 7.8 Kahramanmaraş earthquake on the East Anatolian Fault Zone. Seismicity is composed of isolated spatio-temporal clusters within 65 km of future epicentre, displaying non-Poissonian inter-event time statistics, magnitude correlations and low Gutenberg-Richter b-values. Local comparable seismic transients have not been observed, at least since 2014. Close to epicentre and during the weeks prior to its rupture, only scarce seismic activity was observed. The trends of seismic preparatory attributes for this earthquake follow those previously documented in both laboratory stick-slip tests and numerical models of heterogeneous earthquake rupture affecting multiple fault segments. More comprehensive earthquake monitoring together with long-term seismic records may facilitate recognizing earthquake preparation processes from other regional deformation transients.
Abstract
Short term prediction of earthquake magnitude, time, and location is currently not possible. In some cases, however, documented observations have been retrospectively considered as ...precursory. Here we present seismicity transients starting approx. 8 months before the 2023
M
W
7.8 Kahramanmaraş earthquake on the East Anatolian Fault Zone. Seismicity is composed of isolated spatio-temporal clusters within 65 km of future epicentre, displaying non-Poissonian inter-event time statistics, magnitude correlations and low Gutenberg-Richter
b
-values. Local comparable seismic transients have not been observed, at least since 2014. Close to epicentre and during the weeks prior to its rupture, only scarce seismic activity was observed. The trends of seismic preparatory attributes for this earthquake follow those previously documented in both laboratory stick-slip tests and numerical models of heterogeneous earthquake rupture affecting multiple fault segments. More comprehensive earthquake monitoring together with long-term seismic records may facilitate recognizing earthquake preparation processes from other regional deformation transients.
Intensive global positioning system (GPS) monitoring after the 1999 İzmit earthquake provides an opportunity to understand the postseismic behaviour of a strike-slip fault and the rheology below the ...brittle upper crust. Two data sets are available: displacements measured during the first 300 days after the İzmit earthquake and velocity measurements between 2003 and 2005. Using an inversion method and a forward modelling, respectively, we investigate two mechanisms: (1) afterslip on and below the coseismic rupture plane and (2) viscoelastic stress relaxation in the lower crust and upper mantle described by a Maxwell or a standard linear solid (SLS) rheology. The inversion results show that the first several months following the İzmit earthquake were dominated by afterslip at depths shallower than 30 km and the slip amount decayed with time; after that, apparent afterslip has a very different spatial distribution and is located much deeper. For viscoelastic relaxation, a model with an elastic upper crust and a Maxwell viscoelastic lower crust overlying a Maxwell mantle (E-M-M) fits the data measured in the first 300 days better in the far field than in the near field. However, the observed far-field, 300-day displacement and the long-term (2003–2005) displacement, which might be dominated by viscoelastic relaxation, cannot be described by a Maxwell rheological model with constant viscosity: the effective viscosity increases over time. Therefore, we have built a refined rheological model: an elastic upper crust and an SLS lower crust overlying a Maxwell viscoelastic mantle (E-SLS-M). Our best solution yields a viscosity for the lower crust of ∼2 × 1018 Pa s, a relaxation strength of 2/3 and a viscosity for the Maxwell mantle of 7 × 1019 Pa s. Finally, we explain the data using a composite model, consisting of the preferred E-SLS-M model and the afterslip model obtained from the residual displacement after correcting for viscoelastic relaxation. For the early time period, the residual displacements can be mainly explained by a shallow afterslip whose magnitude decays with time and whose spatial distribution is stable, whereas the residual displacements for the later time period require negligible afterslip. It indicates that the postseismic deformation in the later time period induced by a deep source can be almost entirely explained by the E-SLS-M model. The composite model can generally explain the data in the entire spatial and temporal space.
The submarine Istanbul-Silivri fault segment, within 15km of Istanbul, is the only portion of the North Anatolian Fault that has not ruptured in the last 250years. We report first results of a ...seafloor acoustic ranging experiment to quantify current horizontal deformation along this segment and assess whether the segment is creeping aseismically or accumulating stress to be released in a future event. Ten transponders were installed to monitor length variations along 15 baselines. A joint least squares inversion for across-fault baseline changes, accounting for sound speed drift at each transponder, precludes fault displacement rates larger than a few millimeters per year during the 6month observation period. Forward modeling shows that the data better fit a locked state or a very moderate surface creep--less than 6mm/yr compared to a far-field slip rate of over 20mm/yr--suggesting that the fault segment is currently accumulating stress.
The North Anatolian Fault Zone (NAFZ) is the major transform system that accommodates the westward movement of the relatively rigid Anatolian block with respect to Eurasia. Mitigating the hazard ...associated with devastating earthquakes requires understanding how the NAFZ accumulates and releases the potential energy of elastic deformation both in space and in time. In this study, we focus on the central bend of the NAFZ where the strike of the North Anatolian Fault (NAF) changes from N75° to N105° within less than 100 km, and where a secondary fault system veers southwards within the interior of Anatolia. We present interseismic velocity fields obtained from a Persistent-Scatterers (PS) Interferometric radar analysis of ERS and Envisat radar archives. Despite the high vegetation cover, the spatial density of measurements is high (∼10 PS/km2 in average). Interseismic velocities presented below indicate a velocity change of ∼6-8 mm/yr along the satellite line-of-sight (LOS) mainly centred on the NAF surface trace, and are in good agreement with the GPS velocity field published previously. The observed deformation is accommodated within a zone of ∼20 to 30 km width, in this area where no surface creep has been reported, contrary to the Ismetpasa segment located ∼30 km to the west of this study zone. Although less conspicuous, ∼2-3 mm/yr (∼1 mm/yr along the LOS) of the total deformation seems to be localized along the Lacin Fault. The overall agreement with horizontal GPS measurements suggests that the vertical component of the ground deformation is minor. This is confirmed, over the western part of our study zone, by the 3-D estimation of the ground deformation from the combination of the GPS- and the PS-mean velocity fields. However, a specific pattern of the PS velocity fields suggests that an area, enclosed between two faults with roughly south-north orientation, experiences uplift. The PS analyses of radar time-series both prior and posterior to the Izmit and Dûzce earthquakes indicate that these events did not induce detectable velocity changes in this central bend. The only temporal changes we identify are due to a moderate local earthquake (Mw 5.7, 1996 August 14) whose precise location and coseismic deformation are determined here. Finally, we propose a model of slip-rate distribution at depth along the NAF from the joint inversion of the GPS and PS mean velocity fields. This model suggests a long-term slip-rate of ∼20 mm/yr for a rather uniform locking depth in the range of 15-20 km. However, the locking depth increases to ∼25-30 km in the section comprised between longitudes E34°20' and E34°50'. This lateral evolution is in general agreement with the earthquake distribution at depth from three different catalogues.
We reevaluate the 72 year history of surface slip on the North Anatolian Fault at Ismetpasa since the Mw = 7.4 1944 Bolu/Gerede earthquake. A revised analysis of published observations suggests that ...days after the earthquake the fault had been offset by 3.7 m and 6 years later by an additional 0.74 m. Creep was first recognized on the fault in 1969 as a 0.13 m offset of a wall constructed in 1957 that now (2016) has been offset by 0.52 m. A carbon rod creep meter operated across the fault in the past 2 years confirms results from an invar wire creep meter operated 1982–1991 that surface slip is episodic. Months of fault inactivity are interrupted by slow slip (≤10 µm/d) or multiple creep events with cumulative amplitudes of 2–10 mm, durations of several weeks, and with slip rates briefly exceeding >2.5 mm/h. Creep events accommodate 80% of the surface slip and individually release ≈ 10−6 shear strain on the flanks of the uppermost 3–7 km of the fault. GPS and interferometric synthetic aperture radar methods yield a current fault slip rate of 7.6 ± 1 mm/yr suggesting that creep meters incompletely sample the full width of the surface shear zone. The slip rate has slowed from >10 mm/yr in 1969 to 6.1 mm/yr at present, 4.65 mm/yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates. We calculate that a further 1 m of aseismic surface slip will precede the next major earthquake on the fault assuming an ≈ 260 year main shock recurrence interval on this segment.
Plain Language Summary
We describe slow surface slip on the North Anatolian fault in Turkey, similar to that occurring on the San Andreas and Hayward Faults of California. Rapid slip was initiated by a magnitude 7.4 earthquake in 1944 (several inches/year) but by 1969 it had slowed to less than 1/2″ per year and by 2016 had slowed to 1/4″ per year. The slip occurs in brief episodes at roughly 8 month intervals with durations of a few hours to weeks, and appears to be confined to the uppermost 3 miles of the 7 mile deep fault. When it occurs this slip stresses the top of the region at depth that slips in large earthquakes, suggesting that monitoring surface slip close to the anticipated time of the next earthquake may provide an indication of the imminence of its occurrence.
Key Points
Afterslip decayed rapidly in the first two decades following the 1944 Mw=7.4 Bolu earthquake, and surface slip is now driven almost entirely by plate boundary shear stress
Eighty percent of surface creep (~ 7 mm/yr) on the North Anatolian Fault near Ismetpasa occurs as creep events in the top 5 km
Creep events with 2‐10 mm amplitudes increment stress in the upper 5 km of the Anatolian Fault at ~ 8 month intervals
We present and interpret Global Positioning System (GPS) measurements of crustal motions for the period 1988–1997 at 189 sites extending east‐west from the Caucasus mountains to the Adriatic Sea and ...north‐south from the southern edge of the Eurasian plate to the northern edge of the African plate. Sites on the northern Arabian platform move 18±2 mm/yr at N25°±5°W relative to Eurasia, less than the NUVEL‐1A circuit closure rate (25±1 mm/yr at N21°±7°W). Preliminary motion estimates (1994–1997) for stations located in Egypt on the northeastern part of Africa show northward motion at 5–6±2 mm/yr, also slower than NUVEL‐IA estimates (10±1 mm/yr at N2°±4°E). Eastern Turkey is characterized by distributed deformation, while central Turkey is characterized by coherent plate motion (internal deformation of <2 mm/yr) involving westward displacement and counterclockwise rotation of the Anatolian plate. The Anatolian plate is de‐coupled from Eurasia along the right‐lateral, strike‐slip North Anatolian fault (NAF). We derive a best fitting Euler vector for Anatolia‐Eurasia motion of 30.7°± 0.8°N, 32.6°± 0.4°E, 1.2°±0.1°/Myr. The Euler vector gives an upper bound for NAF slip rate of 24±1 mm/yr. We determine a preliminary GPS Arabia‐Anatolia Euler vector of 32.9°±1.2°N, 40.3°±1.1°E, 0.8°±0.2°/Myr and an upper bound on left‐lateral slip on the East Anatolian fault (EAF) of 9±1 mm/yr. The central and southern Aegean is characterized by coherent motion (internal deformation of <2 mm/yr) toward the SW at 30±1 mm/yr relative to Eurasia. Stations in the SE Aegean deviate significantly from the overall motion of the southern Aegean, showing increasing velocities toward the trench and reaching 10±1 mm/yr relative to the southern Aegean as a whole.
A review on the historical evolution of seismic hazard maps in Turkey is followed by summarizing the important aspects of the updated national probabilistic seismic hazard maps. Comparisons with the ...predecessor probabilistic seismic hazard maps as well as the implications on the national design codes conclude the paper.
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