Murat Utkucu

Crustal thickness variations and isostatic disequilibrium across the North Anatolian Fault, western Turkey

We use teleseismic recordings from a dense array of seismometers straddling both strands of the North Anatolian Fault Zone to determine crustal thickness, P/S velocity ratio and sedimentary layer thickness. To do this, we implement a new grid search inversion scheme based on the use of transfer functions, removing the need for deconvolution for source normalization and therefore eliminating common problems associated with crustal-scale receiver function analysis. We achieve a good fit to the data except at several stations located in Quaternary sedimentary basins, where our two-layer crustal model is likely to be inaccurate. We find two zones of thick sedimentary material: one north of the northern fault branch, and one straddling the southern branch. The crustal thickness increases sharply north of the northern strand of the North Anatolian Fault Zone (NAFZ), where the fault nearly coincides with the trace of the Intra-Pontide Suture; the velocity ratio changes across the southern fault strand, indicating a change in basement composition. We interpret these changes to indicate that both strands of the NAFZ follow preexisting geological boundaries rather than being ideally aligned with the stress field. The thick crust north of the northern NAFZ strand is associated with low topography and so is inconsistent with simple models of isostatic equilibrium, requiring a contribution from mantle density variations, such as possible loading from underthrust Black Sea oceanic lithosphere.

The 2014 Earthquake Model of the Middle East: seismogenic sources

The Earthquake Model of Middle East (EMME) project was carried out between 2010 and 2014 to provide a harmonized seismic hazard assessment without country border limitations. The result covers eleven countries: Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Jordan, Lebanon, Pakistan, Syria and Turkey, which span one of the seismically most active regions on Earth in response to complex interactions between four major tectonic plates i.e. Africa, Arabia, India and Eurasia. Destructive earthquakes with great loss of life and property are frequent within this region, as exemplified by the recent events of Izmit (Turkey, 1999), Bam (Iran, 2003), Kashmir (Pakistan, 2005), Van (Turkey, 2011), and Hindu Kush (Afghanistan, 2015). We summarize multidisciplinary data (seismicity, geology, and tectonics) compiled and used to characterize the spatial and temporal distribution of earthquakes over the investigated region. We describe the development process of the model including the delineation of seismogenic sources and the description of methods and parameters of earthquake recurrence models, all representing the current state of knowledge and practice in seismic hazard assessment. The resulting seismogenic source model includes seismic sources defined by geological evidence and active tectonic findings correlated with measured seismicity patterns. A total of 234 area sources fully cross-border-harmonized are combined with 778 seismically active faults along with background-smoothed seismicity. Recorded seismicity (both historical and instrumental) provides the input to estimate rates of earthquakes for area sources and background seismicity while geologic slip-rates are used to characterize fault-specific earthquake recurrences. Ultimately, alternative models of intrinsic uncertainties of data, procedures and models are considered when used for calculation of the seismic hazard. At variance to previous models of the EMME region, we provide a homogeneous seismic source model representing a consistent basis for the next generation of seismic hazard models within the region.

The 2014 seismic hazard model of the Middle East: overview and results

The Earthquake Model of Middle East (EMME) Project aimed to develop regional scale seismic hazard and risk models uniformly throughout a region extending from the Eastern Mediterranean in the west to the Himalayas in the east and from the Gulf of Oman in the south to the Greater Caucasus in the North; a region which has been continuously devastated by large earthquakes throughout the history. The 2014 Seismic Hazard Model of Middle East (EMME-SHM14) was developed with the contribution of several institutions from ten countries. The present paper summarizes the efforts towards building a homogeneous seismic hazard model of the region and highlights some of the main results of this model. An important aim of the project was to transparently communicate the data and methods used and to obtain reproducible results. By doing so, the use of the model and results will be accessible by a wide community, further support the mitigation of seismic risks in the region and facilitate future improvements to the seismic hazard model. To this end all data, results and methods used are made available through the web-portal of the European Facilities for Earthquake Hazard and Risk (www.efehr.org).

30 Ekim 1983 Horasan-Narman Depremi (Ms=6.8) Yırtılma Özelliklerinin Telesismik Sonlu-Fay Modellemesi Yoluyla İncelenmesi

30 Ekim 1983 Horasan-Narman depremi (Ms=6.8) Kuzeydogu Anadolu Fay Zonu uzerinde meydana gelmistir. Cesitli sismoloji kuruluslari ve arastirmacilarca yapilan onceki nokta-kaynak dalga sekli analizleri, faylanmanin KD-GB uzanimli bir fay boyunca sol yanal dogrultu atimli oldugunu gostermistir. Bu calisma, odaktan 28o ve 92o arasinda episantral uzakliklarda yer alan 17 adet GSN (Global Seismographic Network) istasyonu tarafindan kaydedilmis telesismik uzun-periyod P dalga sekilleri ve Kikuchi vd. (2003) tarafindan gelistirilmis bir sonlu-fay ters cozum yontemi ile sonlu-fay kayma dagilim modelinin bulunmasini amaclamaktadir. Buna gore 45 km uzunlugunda ve 20 km genisliginde bir model fay duzlemi, dogrultu ve egim boyunca sirasiyla 10 ve 5 adet nokta-kaynak kullanilarak tanimlanmistir (nokta-kaynak araliklari esit ve 5 km’dir). Pinar (1995) tarafindan verilen kaynak parametreleri model fay duzleminin baslangic dogrultu (231o), egim (80o) ve kayma acisi (21o) degerleri olarak secilmistir. Calismada odak derinligi 16 km alinmasina ragmen, hem AFAD (Afet ve Acil Durum Yonetimi Baskanligi) hem de ISC (International Seismological Center) tarafindan hesaplanmis episantr lokasyonlari, yirtilmanin hangi yone yayildiginin verice oncellendigini arastirmak icin ters cozumlerde denenmistir. Buna gore AFAD lokasyonunun (KD’ya tek tarafli yirtilma yayiliminin), yuzey kiriklari uzanimi ve artci deprem dagilimi gibi gozlemleri daha iyi aciklayan bir sonuc verdigi gorulmustur. Ters cozum sonuclari, yirtilmanin kucuk bir ters faylanma bilesenli sol-yanal dogrultu atimli faylanma ve cogunlukla derinde oldugunu, dogrultu boyunca yan yana yerlesmis iki puruzun yenilmesi ile kontrol edildigini ve 15 km GB’ya ve 30 km de KD’ya yayildigini onermektedir. Buyuk olan, GB’daki ve 20 km x 10 km yirtilma alanli puruz yaklasik 3.5 m’lik en buyuk kaymaya sahiptir ve yirtilmasi esas olarak odagin GB’sinda kalmaktadir. Odagin KD’sundaki puruz 3 m’lik en buyuk kayma ile 15 km x 10 km’lik bir yirtilma alanini ortmektedir. Yirtilma modeli tum fay boyunca normal faylanma bilesenli 0.5-1.5 m’lik bir sig kaymayi gerektirmektedir. Bu sonuc yirtilma boyunca karsilastirilabilir yer degistirme genliginde yuzey kiriklari gozlemi ile uyumlu olmasina ragmen, normal kayma bileseni beklenmedik olarak dusunulmus ve uzun periyod verilerin dusuk cozunurlugu ile iliskilendirilmistir. Yirtilma modeli icin hesaplanan sismik moment 4.4 x 1019 Nm’dir (Mw≈7.0).

Seismic Hazard in the Marmara Region, Northwest Turkey

The North Anatolian Fault Zone (NAFZ) is a 1500 km-long dextral transform fault that accommodates western extrusion of Anatolian plate resulting from the collision of the Arabian plate in the eastern Anatolia along with sinistral East Anatolian Fault Zone (Reilinger et al. 2006) (Fig. 1a). The North Anatolian Fault Zone bifurcates into and extends as three fault strands, namely the Northern, Middle and Southern Strands, in the Marmara Region (Barka and Kadinsky-Cade (1988); Şaroglu et al. 1992; Armijo et al. 2005) (Fig. 1). The both strands have produced tens of destructive large earthquakes over the past twenty centuries as revealed from the historical sources (Ambraseys, 2002), indicating high seismic activity in the region. In the present study, seismic hazard in the Marmara Region is assessed by examining the historical and instrumental period seismicity and the paleoseismological studies. Also, the b value of the frequency-magnitude distribution (FMD) of earthquakes (Gutenberg and Richter (1944)) in three selected areas (called as Eastern, Western and Southern Areas) in the region is mapped from the declustered background seismicity prior to the August 17, 1999 Izmit earthquake, covering the time period between 1981 and 1999 (Fig. 1).