Self-similarity of the earthquakes occurred in the Eurasia-Arabia collision zone

Depremlerin kaynak mekanizması ve kırılma süreçlerinin incelenmesiyle elde edilen faylanma parametrelerinin birbirleriyle olan ilişkileri sismolojideki temel konulardan biridir. Bu çalışmada Arabistan-Avrasya kıtasal çarpışma bölgesinde meydana gelmiş depremlere ait büyüklük, faylanma alanı, gerilme düşümü gibi parametrelerin birbirleriyle ilişkileri incelenmiştir. Sismik momentin, mb ve Ms büyüklükleriyle olan ilişkisi için bölgeye özgü yeni eşitlikler belirlenmiş ve bunların dünya genelindeki depremlerin kullanılmasıyla belirlenenlerden daha farklı olduğu görülmüştür. Ayrıca 20 depreme ait kayma dağılımı modellemesi sonuçlarından yararlanılarak belirlenen, sismik momentin diğer parametrelerle ilişkilerini içeren gözlemsel bağıntılar belirlenmiştir. Bu bağıntılar özellikle tarihsel depremlerin daha iyi anlaşılması açısından önem taşır.Anahtar Kelimeler: Deprem kaynak parametreleri, ölçekleme ilişkileri, aktif faylanma, doğu Akdeniz, güncel levha etkileşimi.The relationship of faulting parameters obtained by analyzing the earthquake focal mechanisms and rupture histories is one of the main topics of seismology. In this study, we have studied the relationship of the parameters such as magnitude, rupture area, stress drop of the earthquakes occurred in the Eurasia-Arabia collision zone. We used two inversion techniques to find out the source parameters. First, the long period and broad-band body waveforms recorded by GDSN stations in the distance rage of 30°?90° were inverted and the fault orientation, centroid depth, seismic moment and source time function of each event were obtained with minimum misfit solution. Second method is the slip distribution inversion using high frequency broad-band data. The fault plane was divided into several sub-faults and rupture history of each sub-faults were described by triangles. Total fault area, rupture propagation in time and overall source time function were then obtained using minimum misfit solution of inversion. The resulting earthquake parameters results were graphed and the least-square relation equations were fitted. These new equations represent the regional behavior of the earthquakes and are different from that of previous studies using global databases. The present equations are important to resolve the parameters of historical earthquakes in the collision zone.Keywords: Earthquake source parameters, scaling laws, active faulting, eastern Mediteranean, current plate interactions

Source mechanism parameters of Gulf of Gökova earthquakes and tsunami risk in the Rodos-Dalaman region

G&ouml;kova K&ouml;rfezi T&uuml;rkiye&rsquo;nin g&uuml;neybatısında Ege Denizi kıyısında yer alan ve b&ouml;lgedeki tektonik ve depremsellik a&ccedil;ısından aktif graben sistemlerinden biridir. Son yıllarda &ouml;zellikle 2004-2005 tarihleri arasında k&ouml;rfez i&ccedil;erisinde bir &ccedil;ok sayıda orta b&uuml;y&uuml;kl&uuml;kte (Mw&sup3;5.0) deprem meydana gelmiştir. Bu &ccedil;alışmada ters &ccedil;&ouml;z&uuml;m teknikleri ve telesismik uzaklıklarda kaydedilen P ve SH dalga şekilleri kullanılarak b&ouml;lgede oluşan g&uuml;ncel depremlerin kaynak mekanizması parametreleri ve fay d&uuml;zlemi &uuml;zerinde meydana getirdikleri kayma dağılımı ve yırtılma s&uuml;re&ccedil;leri modelleri elde edilmiştir. En k&uuml;&ccedil;&uuml;k hatalı kaynak mekanizması &ccedil;&ouml;z&uuml;mlerine g&ouml;re depremler genel olarak D-B doğrultulu normal faylanma mekanizması ile sığ odak derinliklerinde meydana gelmektedirler. Kaynak mekanizması &ccedil;&ouml;z&uuml;mlerinde &ccedil;ok k&uuml;&ccedil;&uuml;k miktarlarda doğrultu atımlı faylanma bileşenleri bulunmaktadır. Telesismik cisim dalgalarının ve yakın alan istasyonların ters &ccedil;&ouml;z&uuml;m ile modellenmesi sonucu elde edilen kayma dağılımı modelleri ise depremlerin olduk&ccedil;a basit şekilli ve dalım y&ouml;n&uuml;nde ilerleyen dairesel kırılmalar ile meydana geldiklerini g&ouml;stermektedir. Ayrıca, Hellenik Yayı&rsquo;nın doğu uzanımı &uuml;zerinde yer alan Rodos adası ve &ccedil;evresinde tarihsel d&ouml;nem i&ccedil;erisinde meydana gelen ve tsunami (depreşim) dalgalarına neden olduğu rapor edilen bir&ccedil;ok sayıda deprem bulunmaktadır. 1481 yılında meydana gelen tarihsel depremler i&ccedil;in sığ su dalgası teorisine dayalı y&ouml;ntemlerle ve GEBCO-BODC batimetri verisi ile tsunami dalga sim&uuml;lasyonları yapılmıştır. Sim&uuml;lasyon sonu&ccedil;ları bu b&ouml;lgede meydana gelen bir depremin daha &ccedil;ok episantıra yakın b&ouml;lgelerde &ouml;rneğin Rodos adası ve &ccedil;evresinde ve G&ouml;kova K&ouml;rfezi - Fethiye kıyılarında etkili tsunami dalgalarına neden olduğunu g&ouml;stermektedir. &nbsp;Anahtar Kelimeler: Anadolu, deprem, G&ouml;kova K&ouml;rfezi, Rodos-Dalaman, sismotektonik, tsunami.The Gulf of Gökova locates in soutwestern Turkey near the Aegean Sea and surrounded by Datça Peninsula to the south, the island of Kos to the west and Bodrum Peninsula to the north. Active deformation in the region has been observed from widespread seismicity, active normal faulting and tectonically generated topography. In recent and historical times, many destructive earthquakes have occurred in southwestern Turkey. Most of the seismic activity is concentrated along the northern branch of Gökova Fault Zone and it is controlled by E-W trending normal fault system. Intense earthquake activity occurred in Gulf of Gökova in August 2004 and January 2005. Source mechanism solutions and rupture histories for 10 earthquakes, of magnitude Mw ³ 5.0 and shallow focal depth (h < 20 km), which occurred in the region during the period 1986-2005, are used to investigate the geometry of faulting in the region. To obtain source mechanisms and slip distributions on the fault plane, we compared the shapes and amplitudes of long period P- and SH- waveforms recorded in the distance range of 30-90 degrees. The seismograms are formed by the combination of direct (P or SH) and reflected (pP and sP, or sS) phases from a point source embedded in a given velocity structure. Receiver structures are assumed to be homogeneous half-spaces. Seismograms were weighted according to the azimuthal distribution of stations. The solutions were also constrained by P-wave first motion polarities of near-field stations. All the distribution of P-wave first-motion polarities on the equal-area projection of the lower focal hemispheres are consistent with the minimum misfit solutions within a few degrees, with the strikes and dips of the nodal planes. We have also obtained earthquake rupture histories and slip distribution on the fault plane using teleseismic broad-band P waveforms. The rupture process were presented as a spatio temporal slip distribution on a fault plane which was divided into M x N subfaults with length dx and width dy. Then, slip-rate function on each sub fault was described by a series of triangle functions with a rise time. Generally, earthquakes initiates with an earthquake cluster activity and continue for a long time in the gulf. This kind of earthquake generation pattern can carry on by weeks or months decreasing in frequency and in magnitude. The kinematics of the deformation is controlled by normal faults with small strike slip components trending E-W, NE-SW and NW-SE directions. Earthquake source mechanism solutions indicate that normal fault mechanism with a strike-slip component have been observed on the E-W oriented graben and normal fault systems in the Gulf of Gökova and they confirm that extension is in a north - south direction that is in a good agreement with the geology and tectonic structure of the region. T-axes directions obtained from source mechanism solutions demonstrate the NW-SE direction of extension as a result of the convergence between the African plate and the Eurasian plate and the westward movement of the Anatolian block. On the other hand, all earthquakes have generally short source duration and uniform rupture propagation along the dip direction and their focal depths are generally less than 15 km and thus we may suggest that seismogenic thickness in this region is about ~10 km. All these slip distribution results show a uniform circular rupture propagation along the dip direction with a short source duration for earthquakes in Gulf of Gökova . On the other hand, the Gulf of Gökova has a real and major tsunami hazard to the lives and population since it is near the Eastern Mediterranean coast. In this study we have also investigated the tsunami wave propagations to obtain time histories of water surface fluctuations and water particle velocities created by historical 1481 Rhodes earthquakes (M~7.0-7.5) in the Eastern Mediterranean sea using TUNAMI-N2 and AVI-NAMI mathematical models based on the method of Okada (1985). The related parameters for the earthquake are adapted by an analogy of current plate boundaries and earthquake source mechanisms obtained by inversion of teleseismic P- and SH- waveforms. The understanding the faulting geometry, tectonic evolutions and source rupture processes along the active fault zones have significant importance on the tsunami generation. The major and well-known seismic generated tsunamis have occurred in Aegean and Mediterranean Seas and these waves affected the coastal regions since historical times. Keywords: Anatolia, earthquakes, Gulf of Gökova, Rodos-Dalaman, seismotectonics, tsunami

Localized crustal deformation along the central North Anatolian Fault Zone revealed by joint inversion of P-receiver functions and P-wave polarizations

The North Anatolian Fault Zone (NAFZ) is a major plate boundary that separates the Eurasian Plate to the north from the Anatolian Plate to the south and is associated with powerful damaging earthquakes. Despite numerous studies of the crust and upper mantle across the NAFZ, our understanding of the exact mechanisms and distribution of deformation with depth is still limited. Accurate models of the crustal velocity structure are key to assess seismic hazard associated with strike-slip deformation. Here, we address this need by employing a novel method that jointly inverts receiver function waveforms and P-wave polarizations to recover S-wave velocity structure from the surface to the upper mantle. The method is applied to a dense teleseismic data set collected across a segment of the central NAFZ in Turkey. The results provide important new constraints on the sedimentary thickness, depth to basement and Moho discontinuity beneath the region. Our estimates of uppermost sedimentary thickness range from 0 km in some areas (e.g. in the Central Pontides) to 6 km in the Çankırı Basin. Smaller basins are scattered along the NAFZ. A similar pattern is observed for the basement depth, with values exceeding 10 km beneath the Çankırı Basin, where the Moho is shallowest with a depth of ∼32 km. The Moho reaches a maximum depth of ∼42 km beneath the Central Pontides. Most other areas have an average Moho depth of 35–38 km. The results reveal clear structural–tectonic relationships in the crust: areas of fundamentally different sedimentary and crustal architecture are bounded by faults and suture zones. The NAFZ appears to accommodate small-scale basin and basement-highs, and acts as a thick-skinned (i.e. full crustal-scale) boundary between laterally displaced crustal blocks to the north and south. Seismicity clusters are centred on areas of low Vp/Vs ratios that may be representative of weak zones.publishedVersio

Multi‐Scale Rupture Growth With Alternating Directions in a Complex Fault Network During the 2023 South‐Eastern Türkiye and Syria Earthquake Doublet

A devastating doublet of earthquakes with moment magnitude MW 7.9 and MW 7.6 earthquakes contiguously occurred in SE Türkiye near the NW border of Syria. Here we perform a potency-density tensor inversion to simultaneously estimate rupture evolution and fault geometry for the doublet. We find the initial MW 7.9 earthquake involved discrete episodes of supershear rupture and back-rupture propagation, and was triggered by initial rupture along a bifurcated splay of the East Anatolian Fault. The second MW 7.6 event was triggered by the earlier MW 7.9 event, and it involved more extensive supershear rupture along a favorably curved fault, and was likely stopped by geometric barriers at the fault ends. Our results highlight the multi-scale cascading rupture growth across the complex fault network that affects the diverse rupture geometries of the 2023 Türkiye earthquake doublet, contributing to the strong ground shaking and associated devastation

Multiscale full waveform inversion

We develop and apply a full waveform inversion method that incorporates seismic data on a wide range of spatio-temporal scales, thereby constraining the details of both crustal and upper-mantle structure. This is intended to further our understanding of crust-mantle interactions that shape the nature of plate tectonics, and to be a step towards improved tomographic models of strongly scale-dependent earth properties, such as attenuation and anisotropy. The inversion for detailed regional earth structure consistently embedded within a large-scale model requires locally refined numerical meshes that allow us to (1) model regional wave propagation at high frequencies, and (2) capture the inferred fine-scale heterogeneities. The smallest local grid spacing sets the upper bound of the largest possible time step used to iteratively advance the seismic wave field. This limitation leads to extreme computational costs in the presence of fine-scale structure, and it inhibits the construction of full waveform tomographic models that describe earth structure on multiple scales. To reduce computational requirements to a feasible level, we design a multigrid approach based on the decomposition of a multiscale earth model with widely varying grid spacings into a family of single-scale models where the grid spacing is approximately uniform. Each of the single-scale models contains a tractable number of grid points, which ensures computational efficiency. The multi-to-single-scale decomposition is the foundation of iterative, gradient-based optimization schemes that simultaneously and consistently invert data on all scales for one multi-scale model. We demonstrate the applicability of our method in a full waveform inversion for Eurasia, with a special focus on Anatolia where coverage is particularly dense. Continental-scale structure is constrained by complete seismic waveforms in the 30-200s period range. In addition to the well-known structural elements of the Eurasian mantle, our model reveals a variety of subtle features, such as the Armorican Massif, the Rhine Graben and the Massif Central. Anatolia is covered by waveforms with 8-200s period, meaning that the details of both crustal and mantle structure are resolved consistently. The final model contains numerous previously undiscovered structures, including the extension-related updoming of lower-crustal material beneath the Menderes Massif in western Anatolia. Furthermore, the final model for the Anatolian region confirms estimates of crustal depth from receiver function analysis, and it accurately explains cross-correlations of ambient seismic noise at 10s period that have not been used in the tomographic inversion. This provides strong independent evidence that detailed 3-D structure is well resolve

3-D crustal structure along the North Anatolian Fault Zone in north-central Anatolia revealed by local earthquake tomography

3-D P-wave velocity structure and Vp/Vs variations in the crust along the North Anatolian Fault Zone (NAFZ) in north-central Anatolia were investigated by the inversion of local P- and S-wave traveltimes, to gain a better understanding of the seismological characteristics of the region. The 3-D local earthquake tomography inversions included 5444 P- and 3200 S-wave readings obtained from 168 well-located earthquakes between 2006 January and 2008 May. Dense ray coverage yields good resolution, particularly in the central part of the study area. The 3-D Vp and Vp/Vs tomographic images reveal clear correlations with both the surface geology and significant tectonic units in the region. We observed the lower limit of the seismogenic zone for north-central Anatolia at 15 km depth. Final earthquake locations display a distributed pattern throughout the study area, with most of the earthquakes occurring on the major splays of the NAFZ, rather than its master strand. We identify three major high-velocity blocks in the mid-crust separated by the Izmir-Ankara-Erzincan Suture and interpret these blocks to be continental basement fragments that were accreted onto the margin following the closure of Neo-Tethyan Ocean. These basement blocks may have in part influenced the rupture propagations of the historical 1939, 1942 and 1943 earthquakes. In addition, large variations in the Vp/Vs ratio in the mid-crust were observed and have been correlated with the varying fluid contents of the existing lithologies and related tectonic structures

Fault-model of the 2017 Kos-Bodrum (east Aegean Sea) Mw 6.6 earthquake from inversion of seismological and GPS data – Preliminary Report

The 20 July 2017 Kos-Bodrum Mw 6.6 normal fault earthquake (AFAD, 2017) at the NW edge of the Quaternary Gökova Bay graben, was a destructive earthquake associated with a small tsunami (Yalciner et al., 2017). In addition, it is the first normal faulting earthquake in the Aegean covered by a dense array of continuous GPS stations which permit a detailed finite fault modeling (FFM). The preliminary seismological evidence (epicenters, hypocenters of the main shock and of the main aftershocks, and focal mechanism of the main shock) deriving from various agencies, data and techniques, indicate a shallow, nearly E-W striking normal faulting, but its details, including its dip (northerly or southerly) are not resolved. On the basis of independent analysis of seismological and geodetic data we obtained Finite Fault Models (FFM), which are very similar and hence describe the “true” fault

Geodetic and seismological analysis of the 2017 Kos-Bodrum Mw 6.5 earthquake (SE Aegean Sea) provides evidence for the evolution of normal faulting in Gökova graben

The epicentral area of the 2017, Mw 6.5 destructive Kos-Bodrum normal faulting earthquake, associated with a small tsunami in a touristic region, is located within the active Gökova graben and represents a case of a previously unrecognized, shallow normal fault without clear geomorphological signature. Analysis of teleseismic body-waveform data and geodetic data, both in the near- and far- field, indicate a well-constrained 25km long and 10km deep south-dipping normal fault which produced small uplift in the Bodrum peninsula. Modeled fault marks the NW edge of the actively extending part of the Gökova graben and was associated with two clusters of aftershocks, while only its eastern part correlates with known active faults. The 2017 earthquake seems to reflect an immature normal fault between Kos Island and the Anatolia mainland, and expansion of the Gökova graben, perhaps through echelon fractures, as is observed in seismic profiles farther east. Activation of normal faults with modest, if any geomorphic signature, hence not easily recognized before the earthquakes seems not unusual in the Aegean area, and represents a major issue for earthquake hazard analysis