North Anatolian Fault Research Articles

Depth‐Dependent Anisotropy Along Northwest Segment of the North Anatolian Fault Zone: Evidence for Paleo‐Tectonic Structures Contributing to Overall Complexity

AbstractThe North Anatolian Fault Zone (NAFZ) is a prominent tectonic structure with a significant impact on the observed active deformation in Türkiye. Detailed knowledge of the seismic anisotropy in the crust and mantle along this nascent shear deformation zone provides insights into the kinematics associated with past and present tectonic events. We employed teleseismic earthquakes observed by the Dense Array North Anatolia seismic network to map 3‐ D variations in crustal and mantle anisotropy in/around the NW segment of the NAFZ. To achieve this, we first performed a harmonic decomposition analysis of P‐receiver functions. The results were then used as a priori information to conduct an anisotropic receiver function inversion with the Neighborhood Algorithm that enabled imaging of the actual orientation and geometry of anisotropic structures. SKS splitting measurements are further used to make a comparison between the anisotropic behavior of crustal and mantle structures. Crustal anisotropy parameters estimated in our analyses/models well identify the signature of deformation caused by accumulated strain in the earthquake cycle through the strike of shallow cutting faults in the brittle crust beneath the NAFZ. Diffuse intense anisotropic energy at lower crustal depths was attributed to lattice preferred orientation of crystals or partially molten lenses elongated along the shear direction. Strong harmonic energy variations beneath the northern part of the Istanbul Zone likely reflect imprints of LPO‐originated frozen fabric at shallow depths (0–20 km) associated with the palaeotectonic Odessa Shelf, Intra‐Pontide Suture Zones or remnants of the Tethys Ocean.

Transition From Late‐Miocene Syn‐Orogenic Extension to Plio‐Pleistocene Corinth Rifting in the Southern Hellenides, Northern Peloponnese, Greece

AbstractThis study investigates the Late Miocene to Pliocene transition from contractional to extensional tectonics in the upper plate of the Western Aegean retreating subduction system focusing on the Northern Peloponnese area, Greece. A new 3D tectonic model based on field data and cross‐sections clarifies the relationship between Corinth Rift (CR) normal faulting and inherited structures of the Hellenides belt. The tectonic history is divided into five stages: (a) Late Oligocene to Early Miocene ductile high‐pressure, low‐temperature metamorphism of the Phyllite‐Quartzite (PQ) Unit in the Hellenic subduction channel, synchronous with emplacement of overlying Hellenides nappes, (b) syn‐orogenic ductile exhumation of the PQ Unit at the subduction interface below the Cretan detachment (24–14 Ma), (c) Late Miocene underplating and vertical exhumation of the PQ Unit accommodated by thinning of the Hellenides nappe stack on low‐angle normal faults (LANFs) rooting into the Cretan detachment, followed by (d) NW‐SE‐trending high‐angle normal faulting, and (e) initiation of Corinth rifting by N‐S extension at 4–3.5 Ma. New results show that the LANFs all pre‐date Corinth rifting, forming above and around the NNW‐SSE‐trending, N‐plunging PQ dome, so that their strike varies from E‐W in the north to NE‐SW further south. Alluvial sediments deposited above E‐W‐striking LANFs are crosscut by early high‐angle CR faults. The northern termination of the PQ dome partially controls the location and segmentation of the CR. The transition from regional contraction to extension is attributed to changes in subduction dynamics at 8–5 Ma and to the SW propagation of the North Anatolian fault.

The Upper Crustal Deformation Field of Greece Inferred From GPS Data and Its Correlation With Earthquake Occurrence

AbstractWe present a new geodetic strain rate and rotation rate model for Greece that has been derived using a highly dense GPS velocity field. The spatial distribution and the resolved rates of the various velocity gradient tensor quantities provided updated constraints on the present‐day upper crustal deformation in the region and revealed new details not reported previously. The spatial distribution of the second invariant demonstrated that the overall magnitude of strain rates is highest across two well‐defined provinces. The first follows the North Anatolian Fault and its two branches within the north Aegean, crosses central Greece and through the Gulf of Corinth it terminates in western Greece, while the second encompasses the extensional province of western Turkey and the eastern Aegean Sea islands. Our estimates revealed that shearing affects some of the fault‐bounded grabens of central Greece that lie to the SW of the North Aegean Basin implying considerable oblique extension. We identified a narrow region of counterclockwise rotation whose location and kinematics have been induced by the net effect across the intersection of the clockwise rotating domains of western and central Greece. The Aegean microplate and the Anatolian plate are separated by a wide transition zone which accommodates the curved stretching of the entire plate system. In both edges of the Hellenic forearc the dominant mode of crustal strain is E‐W extension. We found that earthquakes of M ≥ 5.6 are spatially well‐correlated with high‐strain areas, indicating that strain rate mapping could be used to inform future probabilistic seismic hazard analyses.

Investigation of Radon, Total Electron Content and Linear and Nonlinear Variations of Meteorological Variables Due to Earthquakes: ARIMA and Monte Carlo Modelling

An Integrated Autoregressive Moving Average (ARIMA) - Monte Carlo Simulation (MCS) is proposed to analyze and model the anomalies of atmospheric and ground gases by an earthquake along the North Anatolian Fault Zone (Türkiye). Earthquakes, Soil radon gas and Total Electron Content (TEC) showed simultaneous anomalies. There are positive relationships between these three parameters. Also, positive relations between Rn, meteorology, and atmosphere are detected. The proposed ARIMA model and MCS for the Rn-TEC-Earthquake relationships of the measured data gave statistically significant results. This model and simulation showed statistically significant changes in the effects of microearthquakes, which are more difficult to detect than large earthquakes, especially on the ionospheric TEC.

The Marmara Sea basin as a regional depression constrained from ambient noise correlation tomography

SUMMARY We computed a 3-D shear wave velocity model of the Marmara Sea region from ambient noise tomography. The correlations of up to 8 yr of vertical-component seismic recordings from 80 broad-band stations provided Rayleigh wave group velocity measurements in the period band 6–21 s at more than 1400 selected virtual source–receiver pairs. Rayleigh wave group velocity maps were used to derive a shear wave velocity model through simulated annealing inversion. The resulting crustal model provides coverage of the Marmara Sea along with its surrounding regional tectonic features. This allows for an investigation of the spatial extents of the Marmara Sea on a scale larger than that of basins. The low-velocity structures of the Marmara Sea and the Thrace Basins are coeval to a depth of approximately 9 km. The crustal velocities beneath the Marmara Sea basins exhibit a low vertical gradient and smooth horizontal variations. The regional tectonic structures, such as Istranca Massif, Istanbul and Sakarya Zones, display sharp velocity contrasts with the lower velocity crust beneath the Marmara Sea. The observed low crustal velocities, along with depth variations of the velocity isosurfaces (i.e. 3.4 km s−1) indicate that the Marmara region is a structural depression much deeper and larger than the three basins of the North Marmara Trough. The North Anatolian Fault Zone is unlikely to be the primary factor contributing to the origin of this significant depression, as the basin's development appears to have occurred before the fault propagated into the region.

Estimation of Seismic Attenuation from Ambient Noise Coda Waves: Application to the Hellenic Subduction Zone

ABSTRACT The decay of surface-wave coda in ambient noise cross correlations can facilitate the estimation of seismic attenuation. The coda quality factor (Qc) can be measured in longer period bands using ambient noise cross correlations, which is the main advantage of using them over earthquakes. The classic model of Aki and Chouet (1975) has been applied previously to estimate coda Q in the Alps using ambient noise cross correlations. The Alps represents an ideal environment for ambient noise study, because it has very high and near-uniform station density, and the region is away from oceanic noise sources. However, many regions around the world do not have uniform station density and may be seismically more active than the Alps. One such region is the Hellenic subduction zone (HSZ), because it has a high rate of seismicity, sparser station coverage, and is surrounded by seas from outside and within. In this study, we estimate ambient seismic noise Qc in 2.5–5, 5–10, and 10–20 s period bands for the HSZ, which did not exist previously. Then, we mitigate the effects of lapse time and window length, distance, azimuth, as well as the number of stacked days on the Qc. Mapping of Qc measurements in such a geographically heterogeneous setting poses additional challenges, which we solve using a novel approach that adaptively selects paths based on their lengths and azimuthal distribution. The major tectonic zones are identified in the resulting Qc maps in the form of low Qc such as the North Anatolian fault, the Kefalonia transform zone, the Gulf of Corinth, the volcanic centers, and so on. The results also show a good correlation with large topographical features such as the Hellenides and the Thessalian plains, which have also been noticed from Qc analysis in other parts of the world.

Low temperature thermochronology reveals tilting of crystalline bodies, Halilaga porphyry Cu-Au deposit, NW Anatolia: Implications for exploration of porphyry copper deposits and interpretation of low-temperature thermochronology data for regional tectonics

Because most crystalline bodies lack intrinsic paleo-horizontal information, their tilting cannot be measured directly. Their vertical movement, however, may be tracked by low-T thermochronology (LTT) tools. Because tilting is caused by differential vertical movements, it can be understood if the rate of differential movements is determined. In this regard, here we apply a new LTT-based approach to calculate the orientation of a tilted crystalline body, the Halilaga Cu-Au deposit, in NW Anatolia. Orientation is consistent with the one calculated from a drillhole-based 3D model of the deposit. This reveals the significance of tilting calculations for the exploration of porphyry Cu deposits. On the other hand, and more importantly, it emphasizes the importance of tilting calculations for geological applications such as LTT-based exhumation histories of samples taken from vertical profiles, and paleomagnetic studies. AHe data from the Halilaga deposit reveals the earliest response to the Aegean back-arc extension at ∼ 24 Ma in the north of Western Anatolia. Lastly, thermal models, the new complementary datasets for the tectonic evolution of the region, show that the Halilaga deposit was exhumed to the surface by the coupling effects of Aegean extension and westward propagation of the North Anatolian Fault, which occurred not earlier than 2 Ma.

Tarihi Erzincan Çadırcı Hamamı'nın Deprem Davranışının İncelenmesi ve Günümüze Kadar Ulaşmasının Sebepleri

In this study, the earthquake behaviour of the historical Çadırcı Bathhouse in Erzincan, which is located on the North Anatolian Fault, the most active fault line of Turkey, was investigated. This historical masonry structure has preserved its structural integrity despite being exposed to two earthquakes of magnitude 7.8 in 1939 and 6.7 in 1992. In accordance with the architectural survey studies, the historical building was modelled in 3D in two different types according to shell and solid modelling techniques. According to the results of response spectrum analysis, stress and displacement distributions and modal characteristic parameters of the structure were evaluated. When the analysis results of the models created with the solid model technique and the shell model technique are compared, it is concluded that the shell modelling technique is safe in such studies, considering the analysis time and modelling difficulty. According to the results of the analyses, considering the stress distribution in the historical building elements, it is seen that the configuration characteristics of historical masonry structures are important in earthquake resistance like other building systems.

Post-2023 Türkiye earthquake risk assessment of cascade dams in upper Euphrates basin

The southeastern region of Türkiye faced two significant earthquakes on February 6, 2023, causing widespread destruction and substantial damage to various infrastructures. Over forty large dams in the region were affected, leading to potential new earthquake-prone areas due to energy accumulation in neighboring regions. This study focuses on the seismic risk of eight cascade dams on the Peri River, a tributary of the Euphrates main river, following these earthquakes. The dams, including Kalecik, Kigi, Konaktepe, Ozluce, Pempelik, Seyrantepe, Tatar, and Uzuncayir, with heights ranging from 31 m to 146 m, are situated in a region influenced by the North Anatolian Fault Zone. The research advocates for a comprehensive re-analysis of certain large dams, considering the updated seismic specifications and seismological maps of Türkiye. The study explores the hazard and overall risk assessment of these dams, emphasizing the cascade system and highlighting the critical seismic vulnerabilities of Kigi and Ozluce dams, with a particular focus on their implications for water security in the region. Our findings underscore the need for tailored safety measures for each dam, focusing on early defect detection. By adopting a proactive stance and implementing our recommendations, the resilience of these dams can be enhanced, contributing to the overall water security of the region.

Evaluation of November 23, 2022, Duzce Earthquake data with Ground Motion Prediction Equations

An earthquake with a magnitude of 5.9 Mw occurred in Düzce (Gölyaka) on November 23, 2022. A rupture occurred on the Karadere Segment, which is a section of the North Anatolian Fault zone. According to the investigations, an 8 km section that was not broken in the 1999 Gölcük Earthquake was broken by this earthquake and caused the earthquake. Station number 8105, one of the stations of the Disaster and Emergency Presidency, measured the maximum ground acceleration of the earthquake as 0.6g. This value is above the PGA value taken from the hazard map of the region. This earthquake in the Marmara region attracts the attention of researchers both because it is close to the 1999 Gölcük Earthquake and because there is an earthquake expectation in Istanbul and its surroundings. Ground motion prediction equations are created by researchers to predict the effects of future earthquakes. The aim of this study is to compare the earthquake data considered in the study with 5 of the ground motion equations developed for Turkey. PGA data were collected and compared with the 5 attenuation relations used from the stations taking measurements from the earthquake, and the compatibility of the earthquake with the 5 existing models was examined. As a result of the study, it was determined that among these attenuation relations, the attenuation relations prepared using the data in the region where the earthquake occurred showed a higher fit. In addition, it has been observed that low pga values at stations farther from the epicenter of the earthquake fit better with the curves obtained from the attenuation relations. The number of data sets used in attenuation relations and the study area increase the possibility of estimating earthquake parameters. The data set used in the AR4 attenuation relationship used in the study and the fact that the region taken into consideration is the region where the earthquake occurred increased the data-model compatibility. It was concluded that existing attenuation relationships should be updated in order to better predict future earthquakes and their effects.

The September 26, 2019 Silivri Earthquake (Mw=5.6), NW Türkiye

The September 26, 2019 Silivri earthquake (MW=5.6-5.8) occurred along the North Anatolian Fault Zone segments extending beneath the Marmara Sea. In the present study the teleseismic P waveforms and 20-year long background seismicity of the earthquake (MW=5.6-5.8) have been analyzed. Point-source inversion of the teleseismic P waveforms revealed that the earthquake was due to oblique faulting and released a seismic moment of 3.2 x 1017 Nm (MW=5.6). The frequency-magnitude distributions (FMDs) for the background seismicity have been calculated for 5-year long time windows after the 1999 İzmit earthquake. The considerable decrease of b-value of the FMDs just before the 2019 Silivri earthquake has been interpreted as stress increase along the fault segments which provides a reasonable clue for the occurrence of the earthquake. The FMD distribution for the 5 year-long time windows before the 2019 Silivri earthquake suggests a recurrence time interval of 168 years and occurrence probability of %16 within the next 30 years for a Mw=7.5 earthquake.

Sapanca Gölü Yakınında Tek Bir Sismik İstasyonda Tekrarlayan Deprem Gözlemleri

The North Anatolian Fault Zone (NAFZ), which forms the plate boundary between Anatolian Plate and Eurasian Plate, is one of the most active transform fault zones in the world. Following two consecutive magnitude M>7 earthquakes in 1999, an intensified monitoring of western portion of NAF is commenced. Dense networks of onshore/offshore seismic, acoustic, geodetic sensors and surface creep and strain sensors were installed. A single seismic sensor among these, which is located at the midpoint of 1999 ruptures, near Lake Sapanca, exhibits some unusual seismic activity. On a fault segment where creep is known to be present, a series of minor seismic events was observed with identical locations and a recurrence time of three years. These events are quite short in duration and highly similar in their waveforms. Using a single station approach, their angle of incidence and back azimuth were found to coincide with the location of two M2.3 and M2.1 events. At this stage, it is not clear whether these events reflect fault creep at seismogenic depth. Nevertheless, these initial observations emphasize the necessity of monitoring this segment more densely, where recurrent minor earthquakes are likely to be observed.

Seismic activations in Turkey in the 17th – early 21st centuries and Kahramanmarash earthquakes on February 6, 2023

The long-term seismic regime of Turkey for the 17th - early 21st centuries are analyzed. It is shown that the fundamental feature of the seismic regime is periodic seismic activations (SA) of strong earthquakes. During the analyzed period, 14 seismic activations of various durations (from 4 to 24 years) and a different number of events (from 4 to 22) were traced. The last SA in Turkey began in 2011, and most likely did not end with the Kahramanmarash earthquake in 2023. SA, as a rule, involves the main seismically active regions of the country (the Aegean coast, the North and East Anatolian faults), but with a clear dominance a certain seismically active area with reduced activity of others. An analysis of historical seismicity shows that strong earthquakes along the North and East Anatolian faults in many cases occur in the same source zones, confirming the concept of seismic sources as inherited geological structures, which may serve as an important prognostic symptom. The Kahramanmaraş earthquakes on February 6, 2023 occurred in the framework of the seismic activation that began in 2011.The position of the Mahmaranmarash seismic source on the southern segment of the East Anatolian fault is in good agreement with displacement of seismic sources from north to south along this fault in the 20th century.

Newly discovered, the Kayapa-Yenişehir cross-basin fault: As revealed by geological and geophysical studies along the southern branch of the North Anatolian Fault Zone, a possible source of the destructive 1855 Bursa earthquakes

This study presents our geological and geophysical findings about a right-lateral cross-basin fault (Kayapa-Yenişehir Fault-KYF) formed in the composite Bursa-west, Bursa-east, and Yenişehir pull-apart basins on the southern branch of the North Anatolian Fault Zone around Bursa in southern Marmara. We examined the compatibility of our observations with various models proposed in the literature.The right-lateral KYF has slip rates of a maximum of 8.8 mm/year and a minimum of 3.0 mm/year, according to our GPS-based block modeling, and it seems to be related to the latest destructive 1850 and 1855 earthquakes around Bursa. The damage distribution of these earthquakes allows interpretation that only the western part of the KYF was ruptured. The slip rates obtained from the block modeling combined with 621 years since a 1400 CE earthquake suggest that 5.5 m of displacement has accumulated on the eastern 55 km of the KYF. These parameters suggest a magnitude 7.0 or greater earthquake is possible.

Hydration State and Rheologic Stratification of the Lithospheric Mantle Beneath the North Anatolian Fault, Turkey

AbstractWe present constraints on the hydration state and rheology of the lithospheric mantle beneath the North Anatolian fault zone (NAFZ). Peridotite xenoliths from the Biyikali and Çorlu volcanic centers record deformational microstructures consistent with shearing in a lithosphere‐scale transcurrent fault system. Analysis by Fourier transform infrared spectroscopy indicates that nominally anhydrous phases retain some OH−, but bulk rock concentrations are generally restricted to <50 ppm H2O by weight. From the rock microstructure, we determined differential stress magnitude and active deformation mechanism(s); combined with estimates of hydration state, we constrained the rheology. Recrystallized grain size piezometry shows that the mantle beneath the NAFZ sustained differential stresses of 10–20 MPa, largely independent of depth. The dominant deformation mechanism(s) change with depth; xenoliths extracted from shallower depths record evidence for grain size‐sensitive creep possibly in the presence of melt. At intermediate depths, both dislocation creep and grain size‐sensitive mechanisms were active, and we did not observe evidence for deformation in the presence of melt. The deepest samples were dominated by dislocation creep. The strong temperature sensitivity of creep mechanisms, combined with the low variability in differential stress, contributes to a stratified viscosity profile ranging from 1018 Pa s for the deepest samples to >1022 Pa s at shallower depths (assuming a melt‐free rheology). Although difficult to quantify from the rock record, melt likely reduced the viscosity of the shallow lithospheric mantle. Vertical stratification in viscosity beneath the NAFZ, the result of melt‐present deformation and/or transitions in the dominant deformation mechanism, has important consequences for the seismic cycle of strike‐slip fault systems.

Late Quaternary deformation in the western extension of the North Anatolian Fault (North Evia, Greece): Insights from very high-resolution seismic data (WATER surveys)

Since the Pliocene, rift basins have developed in the North Evia region at the south-western extension of the North Anatolian Fault. North Evia, therefore, is a key area for investigating Plio-Quaternary deformation within the diffuse Anatolian-Aegean–Eurasian plate boundary. In this study, we present a detailed map of offshore faults in the North Evia region based on three seismic reflection surveys: an airgun (2004) and two very high-resolution Sparker (2017 and 2021) single-channel surveys. Careful and systematic interpretation of these datasets revealed i) the identification of a new basin (Skiathos Basin) located at the western extension of the North Anatolian Fault and ii) two main fault sets striking oblique to the active N–S-directed extension. The seismicity analysis of the study area reveals pure strike-slip displacements along faults previously identified as normal. The NW–SE-striking faults bordering the North Evia Gulf rift are characterised by left-lateral displacements, and the NE–SW faults present dextral focal mechanisms, following the kinematic character of the North Anatolian Fault. We show that dextral strike-slip deformation recently occurred (in the late Quaternary) in the south-western extension of the North Anatolian Fault, suggesting the significant role of this fault system in the complex structural development of the North Evia region.

Tectonic geomorphology of Türkiye and its insights into the neotectonic deformation of the Anatolian Plate

Quantitative geomorphic analyses are usually powerful in identifying active tectonics across global orogenic belts. Our present study will focus on the Anatolian Plate which hosts a lot of recent catastrophic earthquakes in Türkiye. Six geomorphic indices for 100 sub-basins around Türkiye have been computed including local relief, slope, normalized steepness index (kSn)), hypsometric curve and integral (HI), transverse topographic symmetry factor (Tf), and the basin asymmetry factor (Af). The averaged kSn and Af values have shown four high-value anomalous zones, suggesting relatively high uplift rates featured by high river incision and regional tilting. The values of 0.35 ​≤ ​HI ​< ​0.6 for basins with S-shaped curves imply intensive tectonic activities along the eastern part of the North Anatolian Fault Zone (NAFZ), the Northeast Anatolian Fault Zone (NEAFZ), the East Anatolian Fault Zone (EAFZ), and the Central Anatolian Fault Zone(CAFZ). All results of the geomorphic indices analysis suggest a relatively high degree of tectonic activity in the following four areas, the Isparta Angle, the Eastern Black Sea Mountains, the South-eastern Anatolia Region, and the Central Anatolian fault zone. We further suggest that the eastern part of the NAFZ, NEAFZ, EAFZ, and CAFZ will be more active in tectonic activities, with a greater potential for strong earthquake occurrence.

Slip Partitioning Across Subparallel Strands of the North Anatolian Fault in the Marmara Region

Summary Marmara Region hosts a substantial part of the inhabitants in Turkey, more than 30% of the total population in the cities of Istanbul, Bursa, and Kocaeli. This region has experienced several large earthquakes in the past and is still under threat of destructive earthquakes in the future. There, subparallel strands of the North Anatolian Fault (NAF) expand into the region, distributing the earthquake hazards across the whole region. Thus, it is a key issue to investigate how the tectonic process is distributed between these subparallel strands to discriminate their individual earthquake hazards. In this context, we used GPS slip rates to quantify the slip partitioning of the subparallel strands of the fault system. In addition to available slip rates compiled by Bulut et al. (2019) and Kreemer et al. (2014), we analyzed 71 GPS sites (51 continuous and 20 campaign-based) to intensify the GPS network in the region. GPS observations reveal 81.7%, 7.7%, and 10.7% slip ratios for northern, middle, and southern strands. Time series analysis for four continuous GPS stations in the western Marmara Region also confirms these ratios.

Provenance of far-traveled nappes in the eastern Mediterranean (Uppermost Unit, Crete): constraints from U–Pb zircon ages of detrital and igneous zircons

New U–Pb ages of detrital and igneous zircons of the Uppermost Unit of Crete shed light on its provenance and on Eohellenic to Eoalpine imprints in the eastern Mediterranean. The detrital zircons of all nappes show Variscan ages and are characterized by a Minoan-type age spectrum, which is typical for the NE margin of Gondwana. Parts of the metasedimentary rocks are unexpectedly young. Their detrital zircon ages continue via the Permian until the Late Triassic, Middle Jurassic and Early Cretaceous. The high-grade metamorphic rocks of the Asterousia crystalline complex are likely equivalents of the low-grade metamorphic trench and fore-arc deposits of the Vatos nappe pointing to Late Cretaceous slab roll back. The presence of both late Permian detrital zircons and Late Cretaceous arc-type granitoids suggest that the Uppermost Unit of Crete is derived from the late Permian/Late Cretaceous magmatic belt situated north of the Sava–Vardar–Izmir–Ankara Suture in the Strandja–Rhodope area. To achieve their recent position on Crete, the nappes had to travel more than 500 km. The traveling path is well tracked by rocks of the Upper Cycladic Unit, which are similar to those of the Uppermost Unit of Crete. The large displacement of the Cretan nappes was controlled not only by nappe transport, but probably also by dextral strike–slip along the North Anatolian Fault Zone and related counterclockwise rotation of the Anatolian block since the Eocene.Graphical abstract

Imaging the Crustal and Upper Mantle Structure of the North Anatolian Fault: A Transmission Matrix Framework for Local Adaptive Focusing

AbstractImaging the structure of major fault zones is essential for our understanding of crustal deformations and their implications on seismic hazards. Investigating such complex regions presents several issues, including the variation of seismic velocity due to the diversity of geological units and the cumulative damage caused by earthquakes. Conventional migration techniques are in general strongly sensitive to the available velocity model. Here we apply a passive matrix imaging approach which is robust to the mismatch between this model and the real seismic velocity distribution. This method relies on the cross‐correlation of ambient noise recorded by a geophone array. The resulting set of impulse responses form a reflection matrix that contains all the information about the subsurface. In particular, the reflected body waves can be leveraged to: (a) determine the transmission matrix between the Earth's surface and any point in the subsurface; (b) build a confocal image of the subsurface reflectivity with a transverse resolution only limited by diffraction. As a study case, we consider seismic noise (0.1–0.5 Hz) recorded by the Dense Array for Northern Anatolia that consists of 73 stations deployed for 18 months in the region of the 1999 Izmit earthquake. Passive matrix imaging reveals the scattering structure of the crust and upper mantle around the North Anatolian Fault zone over a depth range of 60 km. The results show that most of the scattering is associated with the Northern branch that passes throughout the crust and penetrates into the upper mantle.