Kandilli Observatory Research Articles

Chaos and Periodicities in Solar Flare Index from Kandilli Observatory during 1976–2014

The Solar Flare Index is regarded as one of the most important solar indices in the field of solarterrestrial research. It has the maximum effect on Earth of all other solar activity indices and is being considered for describing the short-lived dynamo action inside the Sun. This paper attempts to study the short as well as long-term temporal fluctuations in the chromosphere region of the Sun using the Solar Flare Index. The daily Solar Flare Index for Northern, Southern Hemisphere and Total Disk are considered for a period from January 1976 to December 2014 (total 14 245 days) for chaotic as well as periodic analysis. The 0–1 test has been employed to investigate the chaotic behavior associated with the Solar Flare Index. This test revealed that the time series data is non-linear and multi-periodic in nature with deterministic chaotic features. For periodic analysis, the Raleigh Power Spectrum algorithm has been used for identifying the predominant periods within the data along with their confidence score. The well-known fundamental period of 27 days and 11 years along with their harmonics are well affirmed in our investigation with a period of 28 days and 10.77 years. The presence of 14 days and 7 days periods in this investigation states the short-lived action inside the Sun. Our investigation also demonstrates the presence of other mid-range periods including the famous Rieger type period which are very much confirming the results obtained by other authors using various solar activity indicators.

Discrimination of earthquakes and quarries in Kula District (Manisa, Turkey) and its vicinity by using linear discriminate function method and artificial neural networks

In this study, seismic events in Kula district (Manisa, Turkey) and its vicinity have been investigated and then natural and artificial seismic activities are discriminated. Total of 77 digital vertical component velocity seismograms of seismic activities with M L ≤3.5 magnitude from seismic activity catalogs between 2009 to 2014 recorded by Manisa Kula (KULA) broadband station operated by Bogazici University, Kandilli Observatory and Earthquake Resarch Institute Regional Earthquake- Tsunami Monitoring Center (RETMC) were used in this study. The maximum S-wave and maximum P-wave amplitude ratio (Ratio) of vertical component velocity seismograms and power ratio for (1 and 12 sec.) (Complexity-C) and total signal duration (Duration) of the waveform were calculated. The earthquakes and the quarry blasts have been discriminated using linear discriminant function (LDF) and Back Propagation-Feed Forward Neural Networks (BPNNs) that is one of the learning algorithms at the artificial neural networks (ANNs) methods taking correlation between these parameters into consideration. 39 (51%) of the 77 seismic activities were identified as quarry blasts and 38 (49%) of them as earthquakes LDF and ANNs methods have been applied together for the first time for Ratio-C, Ratio-logS and Ratio-duration parameter pairs with the data of Manisa and surroundings, and earthquakes and quarry blasts have been distinguished from each other. LDF and ANNs methods were compared for each pair of parameters. Both of two methods are successful but the ANNs method has higher accuracy percentage values than LDF method when there is sufficient number of data. The accuracy percentages are different for a pair of Ratio versus C, for a pair of Ratio versus logS and for a pair of Ratio versus duration, respectively.

AFYONKARAHİSAR İLİ İÇİN POİSSON VE GUMBEL DAĞILIM MODELLERİ İLE DEPREM TEHLİKE ANALİZİ

Bu çalışmada 1900-2019 yılları arasında Afyonkarahisar ve çevresinde meydana gelen depremlere ait veriler dikkate alınarak deprem tehlike analizleri gerçekleştirilmiştir. Bu amaçla Boğaziçi Üniversitesi Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü veri tabanından temin edilen, büyüklüğü Mw ≥ 4.0 olan 404 adet deprem verisi kullanılmıştır. Veriler Afyonkarahisar merkezli (38.75° Kuzey Enlemi ve 30.53° Doğu Boylamı) 130 km yarıçaplı dairesel bir alanı kapsamaktadır. Deprem tehlikesinin ortaya konulması amacıyla sismoloji literatüründe kabul gören Gutenberg-Richter Büyüklük-Frekans bağıntısı kullanılmıştır. Farklı büyüklükteki depremlere ait tekrarlanma periyotları ve her büyüklük değeri için deprem tehlikesi Poisson ve Gumbel Uç Değerler dağılım modelleri ile çözümlenmiştir. Farklı kabullere dayanan iki dağılım modelinden elde edilen sonuçlar karşılaştırılmıştır.

Computation of monthly runoff coefficients for Istanbul

Water demand for Istanbul is supplied both by impounded reservoirs located within its provincial boundaries and by water transfer from Western and Eastern regions in peripheral areas, located in South-West Black Sea region. The runoff coefficient defined as the ratio of the streamflow to the precipitation, plays a key role in the calculation of the surface water yield of water catchment areas. In this paper, we present the computation of monthly runoff coefficients for an accurate estimation of the yield of the catchment areas. We obtain statistical parameters for monthly temperatures and precipitation, based on 105-year data recorded at Istanbul Kandilli Observatory, modeled as Gaussian and Rayleigh distributed random variables, respectively. We run simulations to predict temperatures and precipitation over a horizon extending to 2100. We apply Turc?s formula and Thornthwaite method to obtain monthly runoff coefficients based on long-term data. The results are compared and discussed with the findings of previous researches.

Lake Van (Southeastern Turkey) Experiment: Receiver Function Analyses of Lithospheric Structure from Teleseismic Observations

The P and S wave receiver functions and their joint inversions are used to study the lithosphere beneath the Lake Van region using approximately 600 teleseismic earthquake data (Mw ≥ 5.8) at different azimuths collected from 10 permanent broadband stations operated by Kandilli Observatory and Earthquake Research Institute and Disaster and Emergency Management Authority in the region. The dataset is taken from the European Integrated Data Archive. The simulated annealing method is used for the joint inversion of P-wave and S-wave receiver functions, since the P410s phase cannot be detected reliably in the depth stacks. This may be due to the low olivine content and high basalt content at this depth. The inversion process is therefore performed without travel time residuals. The crustal thickness is observed at nearly 45 km in all the velocity models obtained from the inversion. The relatively low-velocity layer (Vs = 3.4 km/s) at depths of the middle crust may be associated with volcanic centers near Nemrut, in the west of the region. Additionally, another low-velocity layer (Vs = ~ 3.0 km/s) is observed in the upper crust around the Suphan Volcano. Also, Vp/Vs and Poisson’s ratios are calculated for the study area. Their high values (Vp/Vs ≥ 1.85, and σ ≥ 0.285) correspond to the partial melting of the lower crust in the region. According to velocity models obtained from the inversion results, the most important outcome is that the average variance of the Moho discontinuity (~ 45 km) and lithosphere–asthenosphere boundary (~ 90 km) under the seismograph stations can be interpreted as a likely part of the Arabian oceanic plate in relation to the collision zone.

A conceptual model to increase the visibility and usage of cultural heritage objects: The case of UNESCO’s Memory of the World list1

Abstract Cultural heritage connects the past with the future by forming an integral part of the identities of societies. Thus, countries must protect their cultural heritage and create policies to ensure that people benefit today and pass the heritage on to future generations. Beyond physical protection in the face of globalization, increasing access to cultural heritage is necessary to ensure participation and evaluate practices from an international perspective. Advances in computer and communication technologies are being exploited for these requirements. Acquiring knowledge about and interacting with cultural objects in any part of the world today is possible through the digital humanities approach. In this study, a conceptual model was formed to increase visibility and usage of Kandilli Observatory and Earthquake Research Institute Manuscripts, the Hittite cuneiform tablets from Bogazköy, the works of Ibn Sina at the Süleymaniye Manuscript Library, Evliya Çelebi’s ‘Book of Travels’, and the Old Assyrian Merchant Archives of Kültepe registered in UNESCO’s Memory of the World List. In this model, which is prepared with the digital humanities approach, best practices applied in the field are considered as examples in the literature. Suggestions are made on how to utilize digital humanities tools to increase access and visibility by revealing the economic, social, and cultural values of the works based on the model.

The relationship between TEC and Earth’s magnetic field during quiet and disturbed days over Istanbul, Turkey

In this study, the impact of Earth’s magnetic field on total electron content (TEC) was studied by using statistical multiple linear regression model and co-integration method. TEC values were measured over the Turkey-Istanbul (ista) station using date of global positioning system (GPS), and the magnetic field components of the Earth were measured from Boğaziçi University, Kandilli Observatory and Earthquake Research Institute, Geomagnetic observatory Istanbul (ISK) station. This examination has been carried out during the dates of March 14–19, 2015 covering the dates of March 17–18, 2015 known in the literature as St. Patrick's Day geomagnetic storm. The three days before the storm (March 14–16) were named as quiet days, whereas the other days (March 17–19) were named as disturbed days after which the two periods were examined separately. It was observed as a result of the examination that the x-component (south-north direction) of the magnetic field had a negative impact on TEC on quiet days, whereas the impact was positive on disturbed days. However, the y-component (east–west direction) of the magnetic field had an inverse relationship of the x-component on the quiet and disturbed days. In addition, it was deduced that the impact coefficient of the x and y-component of the magnetic field was higher on disturbed days in comparison with those on quiet days. The correlation coefficient between the TEC and the components of the Earth’s magnetic field was 0.11 on quiet days and 0.95 on disturbed days. Therefore, it can be stated that the relationship of the TEC values with the geomagnetic field are higher on disturbed days.

A Review on Kandilli Observatory and Earthquake Research Institute (KOERI) Seismic Network and Earthquake Catalog: 2008–2018

Abstract. KOERI has a long history of earthquake seismology, beginning its observations right after the devastating earthquake on 10 July 1894 in Istanbul, by deploying the first seismograph in the region. Naturally, its seismic network and earthquake catalog evolved since that time, in harmony with the progress in the science of seismology. Currently, the seismic network consists of 242 stations that record approximately 1500 earthquakes per month during periods of regular seismicity. Magnitude is one of the most critical parameters in determining the size of an earthquake, especially in seismic hazard assessment studies. The objective of this study is to homogenize the magnitudes of the KOERI catalog between 2008 and 2018. For this aim, we computed the Magnitude of Completeness (Mc) for two different time periods between 2008–2011 and 2012–2018 by taking into account the duration magnitude (Md) and local magnitude (Ml), where these parameters might not be available jointly for the both time periods considered. As a result, we present a relationship of Md and Ml magnitudes derived from and applicable to KOERI's earthquake catalogs.

Investigating the consistency of online earthquake catalogs of Turkey and surroundings

There are several national and international online earthquake catalogs publishing the focal parameters of earthquakes in Turkey and surroundings. While international seismological centers provide global earthquake catalogs with data from around the world, as well as their own solutions, local and regional seismic centers are confined to publish regional catalogs with solutions derived exclusively from their own data. In this study, we investigate the consistency of the focal parameters provided by national and international agencies for a large number of earthquakes which occurred in and around Turkey during the period 2000–2017. Agencies that analyze earthquakes in this region on a regular basis and whose data are used in this study are the Bogazici University–Kandilli Observatory and Earthquake Research Institution (BOUN–KOERI; “KOERI” from now on) and the Disaster and Emergency Management Authority, Earthquake Research Directorate (AFAD–ERD; “AFAD” from now on) as well as one of the leading international seismological agencies, the International Seismological Centre (ISC). The study area covers the region bounded by the coordinates 35–42° N and 26–45° E. Estimations of origin times, epicentral coordinates, focal depths, and magnitudes, as well as their uncertainties, provided by AFAD, KOERI, and ISC, are examined. The magnitude values of these three centers are homogenized and checked against each other. Furthermore, the completeness (with regard to magnitude) of each of the tested catalogs is defined, as well as its variation in space and with time. Finally, it is shown that the locations provided by KOERI and AFAD are similar to each other, while ISC solutions are closer to those of KOERI.

Repeating earthquakes and interplate coupling along the western part of the North Anatolian Fault

The Sea of Marmara accommodates segments of the North Anatolian Fault (NAF) in Turkey and remains the only part of the western NAF that has not ruptured during the last century. At its nearest, the segment is ~20 km from Istanbul, the largest city in Turkey. Thus, it is important to understand the locking state of the fault, since it illuminates the strain accumulation rate along the fault segments, which in turn is an important input parameter in seismic hazard studies. To infer the interplate locking state, we used repeating earthquakes that indicate fault creep in the surrounding area using long-term (April 2005 to May 2013) seismic observations at 12 broadband seismic stations operated by Bogazici University Kandilli Observatory and Earthquake Research Institute. We defined repeating earthquakes from waveform coherences that were >0.95 for 40-second-long waveforms of the vertical component. Using the selection procedure, we found 21 repeating earthquakes with magnitude 2.3 to 3.2 that are grouped into 9 sequences. They are distributed along the main NAF, comprising three groups of activity, one group in the Sea of Marmara and a group either side to the east and west. The three groups are located near the boundary of previous large earthquake ruptures, suggesting relatively weak coupling there. We also estimated the fault creep rate from the cumulative slip of the repeating earthquakes using a scaling relationship between repeating earthquakes' moment and slip. The slip rate for these three groups are similar (3–4 cm/yr) and comparable to, albeit slightly higher than, those expected from global plate models (~2.4 cm/yr). This suggests relatively weak locking around the groups. The relocation results of the repeating earthquake hypocenters in the Sea of Marmara suggest the creep is occurring at 10 to 20 km depth. These results suggest heterogeneous coupling in the segment.

Crustal Poisson’s ratio tomography and velocity modeling across tectono-magmatic lake regions of Eastern Anatolia (Turkey): New geophysical constraints for crustal tectonics

The tomography of the Poisson ratio structures based on the Vp/Vs ratio provides much tighter constraints on the crust and uppermost mantle than Vp or Vs alone. In this study, high-resolution crustal tomography beneath tectono-magmatic lake regions (Lakes Van and Erçek) of Eastern Anatolia (Turkey) was used to estimate Poisson’s ratio from the Vp and Vs structures through the joint inversion analyses of the travel times of Vp and Vs using the station records of the permanent network of Kandilli Observatory and Earthquake Research Institute (KOERI, Turkey). The results of Poisson’s ratio anomaly reveal distinct and substantial variations in the different tectonic units and show a prominent, continuous and dense high Poisson’s ratio anomalies in the range of 0.27 to 0.30 for the lowermost crust/the uppermost mantle beneath the regions of Lakes Van and Erçek and comparably low average Poisson’s ratio (∼0.23) anomalies for the brittle crust in several local areas. High Poisson's ratios (over ∼0.29) in the basins of Lakes Van and Erçek and in the vicinity of their boundary faults appear to be due to partial melts. Low Poisson’s ratios (∼0.23) near seismogenetic faults at ∼14 km depth beneath the lake regions suggest weaker and more easily deformable crust. The high and low Poisson’s ratio structures suggest a strongly fault-controlled and highly heterogeneous crustal architecture beneath the lake regions. High Poisson’s ratios at variable depths suggest that the mafic content beneath the lake regions is higher than has ever been expected, thus indicating the existence of intrusive materials of possible mantle origin, interacting with faulted crustal rocks. The regional extent of the high Poisson’s ratios (0.27-0.30) of the lowermost crust/the uppermost mantle proposes strong interaction of partial melts with active tectonics in the basins of Lakes Van and Erçek. Key constraints from the estimated Poisson’s ratios and V-anomalies indicate the diverse and interactive nature of crustal deformations beneath the lake regions where the underplating of the mantle magma scenario is proposed to exert a key control on tectono-magmatic evolution of the regions of Lakes Van and Erçek and serves as a working hypothesis for further studies.

An Investigation on the Evaluation of Regional Earthquake Tsunami Monitoring Center (RETMC) Seismic Network and Catalogue

Seismicity catalogs are the most important product of seismic network operating centers, especially for the earthquake hazard studies. Understanding the nature of regional catalogues has primary importance in shedding light on statistical parameters of the seismicity behavior of that given region. It is a well-known fact that artificial effects exist in the regional catalogues. Precisely determined earthquake parameters are important not only for understanding the seismicity and seismotectonics of a region, but also for providing an accurate estimation of the seismic hazard and risk parameters. In this study, we present an evaluation of the Kandilli Observatory and Earthquake Research Institute (KOERI) - Regional Earthquake Tsunami Monitoring Center (RETMC) seismicity catalog for the time duration of 2013 – 2017. We mapped the magnitude of completeness, Mc, for Turkey for the RETMC catalog. We compared the results with the Mc values of different local earthquake sequences in the region, by also considering the variations of Mc with time. Results of the study will be a reference guide for researchers who benefit from RETMC-KOERI data.

HYPOSEC: a new tool to determine the earthquake fracture mechanism and the October 23, 2011 (Mw = 7.1) Van earthquake, Eastern Turkey and May 24, 2014 (Mw = 6.9) Saros (Northern Aegean Sea) earthquake

Earthquake epicenter distributions do not provide any information on the fault strike alone. To determine the correct fault strike considering the epicenter sequences in these distributions, it is necessary to know both the fault mechanism and the focal depths. The mechanism is of crucial importance with the character of the fault zone in question. However, the depth information is a more efficient parameter for such a purpose. Therefore, one of the procedures that must be carried out for a region with known earthquake parameters is the extraction of the depth section. The earthquake hypocentral section is an important subject of Earth sciences and it is very crucial in active tectonics. Unfortunately, these sections have not been extracted very accurately in the studies so far worldwide. The easy and fast extraction of these cross sections, which are produced from the parameters of epicentral distance and focal depth, is possible through carrying out of the extraction of cross sections by means of a computer. The data sizes used today make this indispensable. HYPOSEC is a Fortran 95 computer code produced for this purpose. The design, running principles, and product of this software program are the subject of this study. HYPOSEC is a robust Fortran code list with a size of 345 KB that uses 16 subprograms composed of 2000 lines. Its version in this study is limited to producing the desired cross-section data. Drawing is not included in this version. The preference for drawing belongs to the user. HYPOSEC is based on an interactive and easy-to-use algorithm. It may use not only a data file compatible with the program’s format (TUREQ3.DAT) but also special data files according to the preference by the user. Besides the extraction of a simple hypocentral depth section, HYPOSEC also allows monitoring the rupture process concerning an earthquake. This operation can be performed according to time or space in parallel with user’s preference. In this study, the HYPOSEC software program is used for both the October 23, 2011 (Mw = 7.1) Tabanli-Van earthquake and the May 24, 2014 (Mw = 6.9) Saros (Northern Aegean Sea) earthquake. For the Van earthquake, it was applied to the aftershocks that occurred within the first 3 months, 6 months, 9 months, 1 year, 1.5 years, and 2 years after the main shock. These data in use belong to the electronic earthquake catalog by Kandilli Observatory and Earthquake Research Institute of Bogazici University. A total of 7766 earthquake data were used during these applications. The cross sections of the different strikes selected according to the faulting strike of the earthquake concerned, its rupture surface, and its relationship with the regional tectonism are extracted by means of HYPOSEC and studied comparatively. Accordingly, a seismogenic zone that subducted northward with a slope of about 25° was activated with the process of the Van earthquake. As also for the Saros earthquake, its consecutive cross section defined the fracture mechanism was made. According to this successive cross section, it was seen that progressing of the fracture mechanism after the main shock had performed as more heavy in the footwall.

Investigation of the crustal and upper-mantle structure of the eastern Pontides orogenic belt (NE, Turkey): a receiver-function study

In this study, we use teleseismic P and S receiver functions (i.e., S-to-P and P-to-S converted signals) and their joint inversions to determine seismic discontinuities in the crust and upper mantle. Eight permanent broadband stations from the KOERI (Kandilli Observatory and Earthquake Research Institute) that are distributed along the eastern Pontides orogenic belt (EPOB), NE, Turkey, comprise our database. Inversion is performed by using a simulated annealing technique with and without travel time residuals. Our inversion results reveal the Moho depth, a high S velocity lid, a low-velocity zone, and the underlying upper mantle layer. The studied area is divided into two regions based on the station locations: (a) a northern region and (b) a southern region. The inversion results from the northern area produce crustal models that indicate that the uppermost crust is represented by a low P and S wave velocity (Vp = ~ 5.0 km/s and Vs = ~ 2.8 km/s). These velocities are clear evidence of (1) the sedimentary and volcanic rocks that widely crop out in the region and (2) a thinner uppermost crust, whereas the velocities of the southern region (Vp = ~ 6.0 km/s and Vs = ~ 3.1 km/s) indicate a thicker uppermost crust (~ 7 km). Our calculated Vp/Vs velocity ratio in the lower crust is approximately 1.90 and 1.80 in the northern and southern regions, respectively. These ratios are generally attributed to mafic rocks. Beneath the northern stations, the crustal thicknesses are 30, 33, 37, and 40 km from east to west, while the depths of the Moho are 46, 42, 39, and 44 km beneath the southern stations. Some velocity histograms show a transition from the high S velocity mantle lid to the low-velocity zone, which is known as the lithosphere–asthenosphere boundary. A representative value of the boundary’s depth is around 83 km in the north and ~ 88 km in the south. The hypothesis of some researchers regarding the existence of southward subduction beneath the eastern Pontides orogenic belt during the Late Mesozoic–Cenozoic is supported by our 2-D and 3-D velocity-depth models.

Turkey and adjacent area seismicity forecasts from earthquake inter-event time mean ratio statistics

The alarm-based forecasting model for earthquakes called moment ratio (MR) is retrospectively tested on Turkey and adjacent area seismicity. This model uses the ratio of the mean inter-event time over the variance as a precursory alarm function to forecast future earthquakes in a given region. In a former study, the MR model was successfully tested in forecasting large earthquakes with magnitude M ≥ 7, occurred in Japan. In this study, it is tested on Turkey and adjacent area seismicity using lower magnitude thresholds, namely by learning from M ≥ 5 events, to forecast earthquakes with magnitude M ≥ 6. For this purpose, a composite earthquake data file is compiled using Kandilli Observatory and Earthquake Research Institute Regional Earthquake and the Tsunami Monitoring Center (KOERI-RETMC) provided catalogs, for the period 1900–2016, and the SHARE European Earthquake Catalog (SHEEC) for the historical period 1000–1899. In this catalog, earthquakes are listed using surface magnitude scale Ms. The time periods used in training and testing are selected by taking into consideration the completeness of the magnitude. Finally, Molchan error diagrams are used to evaluate the forecasting performance of the MR method in practice using a retrospective test. Obtained results are presented as standard MR forecasting maps showing the overall forecasts and optimal maps showing high alarm areas with minimal miss and alarm rates. In addition, the relative intensity (RI) forecasting method is applied to compare different results. Results show MR forecasts outscoring random guessing with good performance compared to RI forecasts. The forecasting maps point to a small high alarm area situated along the Hellenic arc subduction zone east of Crete Island.

Assessment of Aleatory and Epistemic Uncertainty for Ground‐Motion Intensity Measure Prediction in Turkey

Research Article| December 11, 2018 Assessment of Aleatory and Epistemic Uncertainty for Ground‐Motion Intensity Measure Prediction in Turkey Zehra Çağnan; Zehra Çağnan aCivil Engineering Department, TED University, Ziya Gökalp Caddesi, No. 48, Kolej, 06420 Çankaya, Ankara, Turkey, zehra.cagnan@tedu.edu.tr Search for other works by this author on: GSW Google Scholar Sinan Akkar Sinan Akkar bEarthquake Engineering Department, Kandilli Observatory and Earthquake Research Institute, Boğaziçi University, 34684 Çengelköy, Istanbul, Turkey, sinan.akkar@boun.edu.tr Search for other works by this author on: GSW Google Scholar Bulletin of the Seismological Society of America (2019) 109 (1): 263–283. https://doi.org/10.1785/0120180075 Article history first online: 11 Dec 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Zehra Çağnan, Sinan Akkar; Assessment of Aleatory and Epistemic Uncertainty for Ground‐Motion Intensity Measure Prediction in Turkey. Bulletin of the Seismological Society of America 2018;; 109 (1): 263–283. doi: https://doi.org/10.1785/0120180075 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract In this study, we quantify the reduction in total sigma (⁠σtotal⁠) of the Turkish ground‐motion predictive models by partially removing the ergodic assumption. By partitioning residuals into four components: repeatable source‐specific and site‐specific deviations from the population mean as well as site‐corrected within‐event and source‐corrected between‐event parts, event‐corrected single‐station standard deviation (⁠ϕss⁠) and source‐corrected between‐event standard deviation (⁠τss⁠) models were derived. With site correction, σtotal was shown to reduce by 15%. With source correction as well, σtotal was shown to reduce by a further 15% at short‐ and long‐period ranges. The developed aleatory variability models are recommended to be used in hazard assessment studies of single sites under the dominant effect of the North Anatolian fault zone. Last but not least, we quantify the total ground‐motion variability by computing the model‐to‐model variability and statistical‐error components of epistemic uncertainty corresponding to two recent probabilistic seismic hazard assessment efforts for Turkey. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Mantle dynamics beneath Greece from SKS and PKS seismic anisotropy study

SKS and PKS splitting parameters were determined in the broader Greek region using data from 45 stations of the Hellenic Unified Seismological Network and the Kandilli Observatory and Earthquake Research Institute, utilizing teleseismic events that occurred between 2010 and 2017. Data were processed for shear-wave splitting with the Minimum Energy Method that was considered the optimal. The results generally confirm the existence of anisotropic zonation in the Hellenic subduction system, with alternating trench-normal and trench-parallel directions. The zonation is attributed to the upper and lower olivine fabric layers that can, potentially, be present in the subduction zone. At the edges of this zone, two possible toroidal flow cases have been identified, implying the existence of tears that allow the inflow of asthenospheric material in the mantle wedge. The high number of null measurements in the KZN and XOR stations indicates a possible anisotropic transition zone between the fore-arc and back-arc areas. SKS and PKS splitting results are jointly interpreted, given that they yield similar values in most cases.

Investigation of Seismograms of North Korean Nuclear Explosion of September 3, 2017 Recorded by the Sakarya University and Kandilli Observatory Seismic Stations

A nuclear test was done on September 3, 2017 in North Korea. This activity is regarded as a nuclear test based on both CTBTO analysis and the statement of the official North Korean news agency. The type of explosion was announced as a fusion based thermonuclear hydrogen bomb. Preliminary solution of CTBTO International Data Center (IDC) reported the origin time, epicenter coordinates and magnitude as 03:30:01 UTC, 41.3°N 129.1°E, and Mb 6.1. U.S. Geological Survey (USGS) determined these parameters as 41.343°N, 129.036 °E and body wave magnitude, Mb 6.3.In this study the seismograms of September 3, 2017 North Korean nuclear test recorded by the Sakarya University and Kandilli Observatory seismic stations will be investigated.

Probabilistic seismic hazard analysis of Kahramanmaras Province, Turkey

Kahramanmaras and its surroundings are under the influence of East Anatolian and Dead Sea fault zones which have significance in the tectonics of Turkey. The long-term energy accumulation in these zones creates a very high risk level in terms of seismic hazard. In this study, the seismic hazard of Kahramanmaras Province and its vicinity was tried to be determined by using the probabilistic seismic hazard method approach. The earthquake catalog used in the study comprises 424 earthquakes equal or greater than M w = 4.0, covering a time period between 1 January 1900 and 1 January 2015. The earthquake data have been compiled from the catalogs of the International Seismological Center (ISC), Republic of Turkey Prime Ministry Disaster and Emergency Management Precidency (RTPMDEMP), Bogazici University Kandilli Observatory and Earthquake Research Institute. Seismic sources that could affect the study area have been identified according to the Earthquake Model of the Middle East (EMME). Seismic hazard parameters and peak horizontal acceleration values were obtained by using the selected attenuation relationships, and the results were given with iso-acceleration maps corresponding to a recurrence period of 475 years. The calculated peak horizontal acceleration values are generally varying between 0.21 and 0.41 in the study area. The result of this study shows that the southeastern parts of the study area have a greater seismic hazard compared with other parts.

Sunspot group tilt angles from drawings for cycles 19-24

AbstractThe tilt angle of a sunspot group is a critical quantity in the surface transport of magnetic flux and the solar dynamo. To contribute long-term databases of the tilt angle, we developed an IDL routine, which allows the user to interactively select and measure sunspot positions and areas on the solar disc. We measured the tilt angles of sunspot groups for solar cycles 19-24 (1954.6-2017.8), using the sunspot drawing database of Kandilli Observatory. The method is similar to that used in the discontinued Mt. Wilson and Kodaikanal databases, with the exception that sunspot groups were identified manually, which has improved the accuracy of the resulting tilt angles. We obtained cycle averages of the tilt angle and compared them with the values from other datasets, keeping the same group selection criteria. We conclude that the previously reported anti-correlation with the cycle strength needs further investigation.