Kandilli Observatory Research Articles

Kernel Density Estimation for the Interpretation of Seismic Big Data in Tectonics Using QGIS: The Türkiye–Syria Earthquakes (2023)

Numerous studies have utilized remote sensing techniques to analyze seismic data in active areas. Point density techniques, widely used in remote sensing, examine the spatial distribution of point clouds related to specific variables. Applying these techniques to complex tectonic settings, such as the East Anatolian Fault Zone, helps identify major active fractures using both surface and deep information. This study employed kernel density estimation (KDE) to compare two distinct point-cloud populations from the seismic event along the Türkiye–Syria border on 6 February 2023, providing insights into the main active orientations supporting the Global Tectonics framework. This study considered two populations of seismic foci point clouds containing over 40,000 events, recorded by the Turkish Disaster and Emergency Management Authority (AFAD) and Kandilli Observatory and Earthquake Research Institute (KOERI). These populations were divided into two datasets: crude and relocated-filtered. Kernel density analysis demonstrated that both datasets yielded similar geological interpretations. The high-density cores of both datasets perfectly matched, exhibiting identical structures consistent with geological knowledge. Areas with a minimal concentration of earthquakes at depth were also identified, separating different crustal strength levels.

Comparison of a linear discrimination function and artificial neural networks approach to discriminate the seismic events in Ankara (Turkey)

In this study, natural and blast-induced ground vibrations (namely earthquakes and quarry blasts) in Ankara (Turkey) were analysed and distinguished from each other. A total of 156 digitized vertical component velocity seismograms of seismic events of 2009-2014 with Md≤3.5 were obtained from the Lodumlu broadband station (LOD) controlled by Boğaziçi University, Kandilli Observatory, and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center (BU-KOERIRETMC). We examined the following variables: the ratio of the highest amplitude value of the S-wave and the highest amplitude value of the P-wave (Amplitude ratio) of vertical component velocity seismograms, the power ratio (Complexity), the logarithmical value of the amplitude of the S-wave of the seismogram (Log S), and total signal duration of the seismogram. It is the first time that natural and blast-induced ground vibrations were separated from each other using the Fisher’s Linear Discriminate Analysis (FLDA) technique and Artificial Neural Networks (ANNs) approach together in Ankara (The capital of Turkey). Ninety-two (59%) of the 156 seismic events studied were identified as earthquakes and sixty-four (41%) of them were described as blast-induced ground vibrations. Then the obtained accuracy percentage results of three pairs of some variables were compared. The amplitude ratio versus complexity and the amplitude ratio versus total signal duration had a high classification accuracy determination coefficient for the LOD dataset (94% for the FLDA technique and 100% for ANNs approach). ANNs approach is more successful than the FLDA technique.

Characterization of Micro-seismic Activity in Northern Cyprus Using Complexity and Corner Frequency Methods

Cyprus is an island country located in the eastern Mediterranean, to the south of Türkiye and the western of Syria and Lebanon, and is a popular tourist destination. Due to being surrounded by seas on all four sides, meticulous planning of rescue, assistance, and evacuation plans is necessary in the face of disasters such as earthquakes and tsunamis. Tectonically, the southern part of the island is controlled by the Cyprus Arc, while the northern part is dominated by the Kyrenia Range. The demand for raw materials for construction and industry is met through controlled quarry blasting operations carried out by open-pit quarry companies in the districts of Kyrenia and Nicosia. As a result, both natural and artificial seismic events occur in the region, and these quakes are documented in seismic catalogs by seismology centers. However, due to the low energy content of micro-seismic events and the inadequacy of seismic stations on the island, the source types of these seismic events can be misidentified in the catalogs. In this context, the study focuses on 122 seismic events with magnitudes between 0.9≤Ml≤2.7 that occurred in Northern Cyprus during the January 2018 - December 2021 period (4 years). The seismic events recorded by the station LFK, operated by Boğaziçi University Kandilli Observatory and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center (KOERI-RETMC), were classified using Linear and Quadratic Discriminant Functions based on complexity and corner frequency methods. According to the results obtained, 10 of the 122 seismic events were identified as natural, and 96 were determined to be artificial, resulting in a general success rate of 86.89%. However, classification results for 16 seismic events were inconclusive with the methods used. As a result, more detailed secondary analyses should be conducted to accurately determine the source types of micro-seismic events, and the seismic catalogs should be updated accordingly.

Observed Variations and Trends in Temperature Extremes of Longest Meteorological/Climatological Observation Station (Kandilli Observatory) in Turkey (1912-2021)

Bu çalışmada; Türkiye’nin en uzun meteorolojik/klimatolojik gözlemlerine sahip olan Kandilli (İstanbul) Rasathanesi’nde ekstrem sıcaklıkların 1912-2021 dönemindeki değişimleri ve eğilimleri analiz edilmiştir. Çalışmada İklim Değişikliği Tespiti, İzleme ve İndisler Konusunda Klimatoloji Uzman Ekibi (ETCCDMI) tarafından önerilen 14 ekstrem sıcaklık indisi kullanılmıştır. Ekstrem sıcaklık indislerinde olası eğilimleri belirlemede ve eğilimlerin istatistiksel olarak anlamlılığını denetlemede klimatoloji çalışmalarında yaygın olarak kullanılan parametrik olmayan Mann-Kendall (M-K) sıra ilişki katsayısı testinden yararlanılmıştır. Eğilimlerin büyüklüğünü belirlemek için de parametrik olmayan Sen’in Eğim Tahmin (Sen’s Slope Estimation) yöntemi kullanılmıştır. Bunun yanında rasat süresi içinde indislerdeki değişimi belirlemek amacıyla da ekstrem sıcaklık indisleri 1912-1950, 1951-1985 ve 1986-2021 olmak üzere üç alt dönemde incelenmiştir. Analizler sonucunda; soğuk günler ve soğuk geceler indislerinde her on yıl için sırasıyla -0.96 ve -1.04 gün olmak üzere anlamlı azalma eğilimi, sıcak günler ve sıcak geceler indislerinde ise sırasıyla +0.44 gün/on yıl, +0.58 gün/on yıl olmak üzere anlamlı artma eğilimleri saptanmıştır. En düşük gündüz hava sıcaklıkları, en düşük gece hava sıcaklıkları, en yüksek gündüz hava sıcaklıkları, en yüksek gece hava sıcaklıkları indislerinde her on yıl için sırasıyla +0.10, +0.18, +0.5, +0.14 °C olmak üzere artma eğilimleri belirlenmiştir. Minimum rekorlardaki artma eğilimleri istatistiksel olarak anlamlı olmuştur. Don olaylı günler indisinde -0.93 gün/on yıl olmak üzere anlamlı azalma eğilimi, yaz günü (+3.1 gün/on yıl) ve tropikal geceler (+3.4 gün/on yıl) indislerinde ise anlamlı artma eğilimleri tespit edilmiştir. Sıcak dönem süresi indisinde artma eğilimi, soğuk dönem süresi indisinde (-1.37 gün/on yıl) ise anlamlı azalma eğilimleri saptanmıştır. Bu sonuçlar, istasyonda maksimum sıcaklıkların arttığını, minimumların ise azaldığını ortaya koymakta ve bunlara bağlı olarak da sıcak ekstremlerin etkilerinin artığını soğuk ekstremlerinse azaldığını göstermektedir. Diğer taraftan bu sonuçlar, 20. yüzyılın ilk yarısının istasyonun bulunduğu bölge özelinde 1981-2010 normaline göre soğuk olduğunu ancak sıcaklıkların günümüze doğru antropojenik etkilere bağlı olarak giderek arttığını/değiştiğini göstermektedir.

Digitizing Ottoman daily weather observations of Halkali Agricultural School in Istanbul, Turkiye (1896–1917)

AbstractDaily weather observations measured by students and staff at Halkali Agricultural School (a school opened in 1892 on agriculture and animal husbandry during the Ottoman period) from 1896 to 1917 in Istanbul, Turkiye have been transcribed from the original publications into digital form and translated from Ottoman Turkish (the Perso‐Arabic script) to English (Latin alphabet). Over 55,000 observations of daily maximum, minimum and average temperature; rainfall, soil and under soil (0.25 m) temperature; humidity, pressure and wind speed were recovered. In addition, weather observations taken in Kandilli Observatory and Earthquake Research Institute from 1911 to 1936 and taken in Florya Meteorological Station from 1937 to 2022 could inform long‐term temperature changes in Istanbul. The publication of a new historical data set that includes, for the first time, digitized and quality‐controlled daily meteorological observations in Istanbul will enhance the understanding of weather changes in Turkiye back to the late 19th century. These observations will be used to fill gaps in existing temperature and pressure records and to the improvement of the accuracy of reanalysis products prior to the 1950s. It will be the first data set publication of other parameters such as soil temperature, wind speed and humidity for that period in that region. Data are available on the CEDA Archive in csv file format.

Local magnitude determination for Turkey from two independent seismic networks and a consistent M4 + catalogue

SUMMARY Turkish seismicity is routinely recorded by two broad-band seismic networks: the Turkish National Seismic Network (AFAD ‘TU’ network) and the Bogazici University Kandilli Observatory And Earthquake Research Institute (KOERI ‘KO’ network). Each of them has over 200 seismic stations distributed across the country. We obtain a new uniform and consistent local magnitude (Ml) scale for Turkey using data from both networks, as well as the M4 + catalogue with Ml values that results from applying said scale to the events that occurred between 2007 and 2016 within the country. We measure the half peak-to-peak amplitude of the vertical component seismograms and estimate the attenuation parameters through an iterative procedure that fits the logarithm of the amplitude as a function of the hypocentral distance, the local magnitude, the station corrections and a constant accounting for possible systematic differences between amplitudes measured on horizontal seismographs and those measured on vertical seismographs. We additionally scale Ml to the moment magnitude measured by an independent source, obtaining a magnitude relationship accounting for attenuation adjustments, as well as differences between maximum horizontal and vertical amplitudes. The estimated Ml formula shows that station corrections from both networks regionally agree, and that non-zero corrections are centred on zero, within −0.48 and 0.46 magnitude units (corresponding to the 2.5 and the 97.5 quantiles). The new M4 + catalogue with consistent Ml values for AFAD and KOERI shows magnitude residuals that cannot be explained by a Gaussian distribution. We also show a very good agreement between our new Ml value and the original Ml values of AFAD and KOERI, with median differences below 0.1 magnitude units.

Refining micro-seismic catalogs around Seydişehir, Turkey

In Turkey, two official seismology centers, Bogazici University Kandilli Observatory and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center (KOERI-RETMC) and Republic of Turkey Prime Ministry Disaster Emergency Management Authority (AFAD) announce and share seismic catalogs with the public and international services. According to their seismic network distribution, together with different crustal models and calculation algorithms, obtaining earthquake parameters (location, depth, etc.) could differ between these two centers, especially, affecting source types of the low-magnitude events. Both low-magnitude tectonic events and artificial quakes that originating from open-pit quarry are catalogued by the seismology centers. These two centers announce different source types for the seismic events; therefore, this study focuses on the reliable identification of the micro-seismic events. Magnitude Ml<2.4 177 seismic events commonly identified in KOERI-RETMC and AFAD catalogs are used. Due to the differences between KOERI-RETMC and AFAD seismic catalogs, the “first determination” (FD) was needed to start the discrimination analyses. Then, waveforms of the station SEYD and SEDI are operated by KOERI-RETMC and AFAD were analyzed with four methods (Amplitude Ratio, Complexity, Short Time Fourier Transform and Corner Frequency-Power Spectrum) and two statistical approaches (linear and quadratic discriminant functions) with the use and comparison with FD. Finally, station-based weightings are obtained with all techniques, and the source types of all events are calculated in percent. Generally, the success rates of the methods are calculated over 90%. The reliability increases with the co-usage of many analyses and the application of method-based weighting. Hence, many methods should be used to reliably determine the source types of micro-seismic events. Both centers should make more detailed analyses to identify micro-seismic events and share their reliable and revised catalogs.

Upper- to mid-crustal seismic attenuation structure above the mantle wedge in East Anatolia, Turkey: Imaging crustal scale segmentation and differentiation

Multi-frequency P- and S-wave attenuation tomography models of Lake Van area (East Anatolia) have been obtained by estimating coda-normalized wave spectra of 3027 local earthquakes (2.0 < Mw < 7.1). The 6998 waveforms sampled from surface to a depth of 25 km, and were recorded from 2004 to 2020 at seven broadband, three-component digital seismic stations operated by Kandilli Observatory and Earthquake Research Institute (KOERI). We adopted a two-point ray-bending method to trace rays in a 3-D velocity model. We applied the coda normalization (CN) method to P- and S-wave data sets. We inverted the spectral data with a multiple resolution seismic attenuation (MuRAT) approach to obtain final tomographic models. On average, high (low) attenuation corresponds to low (high) velocity anomalies. The P- and S-wave attenuation contrasts delimit four well-known geological zones. High frequency-short wavelength attenuation contrasts constrain the 5-km-deep zone of interaction between magma and sediments within the Lake Van basin. Low frequency-long wavelength attenuation anomalies mark the central section of Lake Van between depths of 10 km and 20 km. This zone coincides with a rigid stable shear zone overlying a possible weak-ductile lower crust, interpreted as a detachment. Both low (5–15 km depth) and high attenuation (>20 km) anomalies mark the area of maximum seismic energy release during the Van event. Their contrast highlights the maximum seismogenetic depth above weak-warm, unstable materials. High attenuation in the SE-part of the Lake Van area coincides with a large hydrothermal and/or magmatic folding-overthrusting, interpreted as a suture-metamorphic complex between depths of 10–15 km. Other minor high-attenuation zones deeper than 5 km focus on complex shear zones in the area damaged by the Van event. The paired attenuation structure of the Lake Van area appears linked to multiple tectonic processes of crust-magma interaction better constrains subsurface segmentation structures and differential deformation types at upper-middle crustal depths.

Seismicity of Turkey and Real-Time Seismology Applications in Determining Earthquake Hazard

Turkey is between three major tectonic plates, is the most active area of the Mediterranean region in terms of earthquake activity. Relative motions between the African, Arabian and Eurasian plates account for most of the tectonic activity in the region. As a result, the Anatolian plate has a high danger for seismicity. This consists of the North Anatolian Fault Zone (NAFZ), East Anatolian Fault Zone (EAFZ) and SE Anatolian Thrust Zone which form the borders of the Anatolian Plate and important active fault segments throughout Western Anatolia. All these active faults cause a short time intervals intensive damages in Turkey earthquakes. In order to investigate and to real-time monitor the seismic activity and seismotectonic of Turkey and its vicinity, The Kandilli Observatory and Earthquake Research Institute (KOERI) of Bogaziçi University and AFAD operates seismic stations countrywide. Observatory has been supplying mainly 3 kind of seismological data: phase readings, waveform and catalogue to the earth scientists in Turkey. Earth science studies have an important contribution to the emergence of earthquake hazard. The evaluation of the data receiving from the seismic stations contributes to the determination of earthquake hazard in detail, and to contribute to the minimization of the risks of the earthquake by developing earthquake catalogues. Also, all of the earthquake parameters after the earthquake, automatically distributed and mapped. After an important earthquake, KOERI and AFAD is quickly sent information from the smartphones to the society and the decision-making institutions carrying out disaster studies.

Statistical analysis of earthquake catalogs for seismic hazard studies around the Karliova Triple Junction (eastern Turkey)

A complete and comprehensive earthquake catalog is a substantial input to do probabilistic seismic hazard analysis. The Karliova triple junction (eastern Turkey) is characterized by an active seismicity mostly in the shallow crust. Origin times, earthquake locations, and magnitudes reported by the Kandilli Observatory and Earthquake Research Institute, Boğaziçi University (KOERI) and three international agencies (ISC, IRIS and EMSC) in the region bounded by latitudes 37.5° and 40.5° N and longitudes 37.5° and 42.5° E have been gathered in order to quantify the seismicity around the study area and calculate associated seismic parameters. The Magnitudes of completeness (Mc) and Gutenberg-Richter (GR) recurrence parameters (a- and b-values) have been estimated. The same Mc value of 2.7 has been obtained for all catalogs. After 2014, all earthquakes with magnitudes higher than 2.0 are reliably recorded. However, the b-value varied from 0.97 to 1.28. High b-value anomalies mostly for earthquakes with shallow depths (5–15 km) have been observed. A relatively lower b-values are found at depths <5 km. The most probable largest annual earthquakes are around Mw = 5.8. The seismic hazard parameters i.e. the maximum regional magnitude mmax, mean seismic activity rate λ, the slope of the frequency–magnitude Gutenberg–Richter relationship, and the β value (bln(10)) have been estimated. Using the Bayesian model for the earthquake occurrence in time and earthquake magnitude, which incorporates seismic information from historical and instrumental catalogs, the hazard parameters are presented in terms of the probability of exceedance for 1- 10- 50- and 100-year return periods with a b-value equal to 1.19 and mmax equal to 8.05. The highest probability of earthquakes, which may occur in an interval of 50 years is estimated as Mw = 7.0. The average recurrence interval of earthquakes with magnitudes 6.7 and 7.8 (the maximum observed magnitudes at KOERI catalog and instrumental earthquakes in the region, respectively) are ∼27 and ∼488 years.

KOERI’s Tsunami Warning System in the Eastern Mediterranean and Its Connected Seas: A Decade of Achievements and Challenges

A tsunami warning system providing services in the Eastern Mediterranean, Aegean, Marmara and Black Seas under the UNESCO Intergovernmental Oceanographic Commission (IOC)—Intergovernmental Coordination Group (ICG) for the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and Connected Seas (NEAMTWS) framework was established in Turkey by the Kandilli Observatory and Earthquake Research Institute (KOERI) (Özel et al., 2011). KOERI’s Regional Earthquake and Tsunami Monitoring Center (RETMC) was established on the foundations of the legacy KOERI National Earthquake Monitoring Center (NEMC) by adding observation, analysis and operational capability related to tsunami early warnings after an extensive preparatory period during 2009 and 2011. The center initiated its test-mode 7/24 operational status as a national tsunami warning center in 2011, and after a one year period it became operational as a candidate tsunami warning center for NEAMTWS on 1 July 2012, together with CENALT (Centre d’Alerte aux Tsunamis—France) and followed by the NOA (National Observatory of Athens—Greece) on 28 August 2012, INGV (Instituto Nazionale di Geofisica e Vulcanologia—Italy) on 1 October 2014 and IPMA (Instituto Português do Mar e da Atmosfera—Portugal) on 1 February 2018, completing full coverage of the tsunami-prone regions monitored by NEAMTWS. In this paper, an overview of the progress and continuous improvement of KOERI’s tsunami early warning system will be presented, together with lessons learned from important tsunamigenic events, such as the 20 July 2017 Bodrum–Kos Mw 6.6 and 30 October 2020 Samos–Izmir Mw 6.9 earthquakes. Gaps preventing the completion of an effective tsunami warning cycle and areas for future improvement are also addressed.

Analysis of the b-Values Before the July 21 th, 2017 Mw 6.6 Bodrum-Kos, Turkey Earthquake

In this study, a statistical analysis of regional and time-dependent changes of earthquake activity in Bodrum and its vicinity before the Bodrum-Kos earthquake (Mw 6.6) that occurred on 21 July 2017 was performed and the Gutenberg-Richter b-value change was investigated. The earthquake catalog used in the calculations was taken from Boğaziçi University, Kandilli Observatory and Earthquake Research Institute. This catalog contains 16947 earthquakes with M&amp;gt;2 between 2004 and the time until the Bodrum-Kos earthquake of 21.07.2017. The completeness magnitude for these earthquakes was calculated as 2.6. The b-value was calculated as 1.25 ±0.01 using the maximum probability method. Considering that tectonic earthquakes have b-values between 0.5-1.5, it is seen that the b-value obtained by Gutenberg-Richter law for the vicinity of Bodrum in this study is a good fit. In addition, it was observed that b-value took high values in the north of Bodrum before the Bodrum-Kos earthquake occurred. Low values are observed in the southeast of Bodrum. Stress accumulation was correlated with b-values for the region.

Periodic Variation of Solar Flare Index for the Last Solar Cycle (Cycle 24)

In this study, we used the flare index (FI) data taken from Kandilli Observatory for the period of 2009–2020. The data sets are analyzed in three categories as Northern Hemisphere, Southern Hemisphere, and total FI data sets. Total FI data set is obtained from the sum of Northern and Southern Hemispheric values. In this study, the periodic variations of abovementioned three categories FI data sets were investigated by using the MTM and Morlet wavelet analysis methods. The wavelet coherence (XWT) and cross wavelet (WTC) analysis methods were also performed between these data sets. As a result of our analysis, the following results were found: (1) long- and short-term periodicities ( 2048 ± 512 day and periodicities smaller than 62 days) exist in all data sets without any exception at least with 95 % confidence level; (2) all periodic variations were detected maximum during the solar cycle, while during the minima, no meaningful period is detected; (3) some periodicities have data preference that about 150 days Rieger period appears only in the whole data set and 682-, 204-, and 76.6-day periods appear only in the Northern Hemisphere data sets; (4) During the Solar Cycle 24, more flare activity is seen at the Southern Hemisphere, so the whole disk data periodicities are dominated by this hemisphere; (5) in general, there is a phase mixing between Northern and Southern Hemisphere FI data, except about 1024-day periodicity, and the best phase coherency is obtained between the Southern Hemisphere and total flare index data sets; (6) in case of the Northern and Southern Hemisphere FI data sets, there is no significant correlation between two continuous wavelet transforms, but the strongest correlation is obtained for the total FI and Southern Hemisphere data sets.

Performance Evaluation of Reinforced Concrete Buildings During the Sivrice-Elazığ Earthquake (Mw=6.8, January 24, 2020) in Accordance with Turkish Earthquake Code

A great number of reinforced concrete building structures were damaged or collapsed during the earthquake that hit Sivrice district of Elazığ city located in the southwest of the Eastern Anatolia Region of Turkey on January 24, 2020. Magnitude of the earthquake were announced as [Formula: see text] and [Formula: see text] by Kandilli Observatory &amp; Earthquake Research Institute (KOERI) and Earthquake Department of the Disaster and Emergency Management Presidency (AFAD), respectively. More than a thousand of aftershocks with the magnitude of 1.2–5.1 occurred between January and February 2020. The magnitude of the structural damage was relatively high compared with the peak value of recorded ground acceleration (2.85[Formula: see text]m/s2) at the epicenter (Sivrice district) of the earthquake. It was determined that 584 buildings were demolished, 6845 were severely damaged, 1207 were moderately damaged, 14,389 were slightly damaged and 14,317 were undamaged. Also, there were 235 buildings that required urgent demolition. In this paper, the performance of the reinforced concrete buildings during the Sivrice-Elazığ earthquake is presented along with time-histories of ground motion records and response spectrums. Observed design and construction practices were carefully evaluated and compared with Turkish Earthquake Code. It was seen that the most significant causes of the failures were due to the poor concrete quality, the use of non-ductile detailing, the poor project design and construction quality. According to field inspections of our technical team, it is concluded that performances of the undamaged buildings following earthquakes do not prove that they have adequate seismic safety.

Evolution of the Kandilli Observatory and Earthquake Research Institute (KOERI) Seismic Network and the Data Center Facilities as a Primary Node of EIDA

AbstractAs the earliest institute in Turkey dedicated to locating, recording, and archiving earthquakes in the region, the Kandilli Observatory and Earthquake Research Institute (KOERI) has a long history in seismic observation, which dates back to the installation of its first seismometers soon after the devastating Istanbul earthquake of 10 July 1894. For over a century, since the deployment of its first seismometer, the KOERI seismic network has grown steadily in time. In this article, we present the KOERI seismic network facilities as a data center for the seismological community, providing data and services through the European Integrated Data Archive (EIDA) and the Rapid Raw Strong-Motion (RRSM) database, both integrated in the Observatories and Research Facilities for European Seismology (ORFEUS). The objective of this article is to provide an overview of the KOERI seismic services within ORFEUS and to introduce some of the procedures that allow to check the health of the seismic network and the quality of the data recorded at KOERI seismic stations, which are shared through EIDA and RRSM.

Orientations of Broadband Stations of the KOERI Seismic Network (Turkey) from Two Independent Methods: P- and Rayleigh-Wave Polarization

Abstract The correct orientation of seismic sensors is critical for studies such as full moment tensor inversion, receiver function analysis, and shear-wave splitting. Therefore, the orientation of horizontal components needs to be checked and verified systematically. This study relies on two different waveform-based approaches, to assess the sensor orientations of the broadband network of the Kandilli Observatory and Earthquake Research Institute (KOERI). The network is an important backbone for seismological research in the Eastern Mediterranean Region and provides a comprehensive seismic data set for the North Anatolian fault. In recent years, this region became a worldwide field laboratory for continental transform faults. A systematic survey of the sensor orientations of the entire network, as presented here, facilitates related seismic studies. We apply two independent orientation tests, based on the polarization of P waves and Rayleigh waves to 123 broadband seismic stations, covering a period of 15 yr (2004–2018). For 114 stations, we obtain stable results with both methods. Approximately, 80% of the results agree with each other within 10°. Both methods indicate that about 40% of the stations are misoriented by more than 10°. Among these, 20 stations are misoriented by more than 20°. We observe temporal changes of sensor orientation that coincide with maintenance work or instrument replacement. We provide time-dependent sensor misorientation correction values for the KOERI network in the supplemental material.

A consistent and high-quality M4+ earthquake catalogue for Turkey 2007–2016 from two independent catalogues

SUMMARYWe describe the process of pairing M4+ earthquakes reported in the routine catalogues of two seismic networks in Turkey and present the resulting products: (i) hypocentre locations and magnitudes and (ii) minimum 1-D velocity model with station delays for the combined station network. The two networks are the Kandilli Observatory (KOERI) and the National Earthquake Department (AFAD) and the data cover the decade 2007–2016. The seismic stations of these two networks spatially overlap within Turkey, and with their average station spacing of about 60 km, they potentially detect all events of magnitude ≥4 independently. We first obtain separate AFAD and KOERI catalogues using a series of joint hypocentre inversions that allow us to detect outliers and problematic events. We establish separate minimum 1-D velocity models and station delays for each catalogue and reduce the average inversion residuals by 75 per cent compared to our first joint hypocentre inversion using the original catalogue event locations. We then pair M4+ events from AFAD (1219) and KOERI (1271) catalogues using a spatiotemporal window and test if the combined observations indeed belong to the same event. In these tests, we compare the hypocentre location residuals of the combined observations to those of the two individual events, apply epicentral distance limits between the individual and the paired events and assess qualitatively a simple probabilistic solution of the events. As a result, we get 1145 paired events. We finally obtain a minimum 1-D velocity model with delays for all seismic stations of AFAD and KOERI combined and relocate the entire set of events. These include all paired events plus M4+ earthquakes reported by AFAD or KOERI that could not be paired (500). The velocity model has a well-defined Moho at a depth of 32 km. The station delays for both networks regionally correspond very well and exhibit some correlation with the regional subsurface temperature field. The well-locatable hypocentres of the new M4+ catalogue have an epicentre uncertainty of 3 km and a depth uncertainty of 4 km. We ascribe to each paired earthquake a magnitude equal to the average of the reported magnitudes by AFAD and KOERI. The new magnitude frequency distribution is similar to those of AFAD and KOERI for M4+ events. Except for events of magnitude larger than 5.5, there is no systematic bias in the magnitudes reported by AFAD and by KOERI, and the standard deviation is 0.3.

Discrimination of earthquakes and quarries in the Edirne district (Turkey) and its vicinity by using a linear discriminate function method and artificial neural networks

In this study, seismic events in the Edirne district (Turkey) and its vicinity have been investigated in order to discriminate earthquakes from quarry blasts. A total of 150 seismic events with Md ≤ 3.5 duration magnitude from a seismic activity catalog between 2009 and 2014 recorded by the Enez (ENEZ), Erikli (ERIK) and Gelibolu (GELI) broadband stations operated by Bogazici University, Kandilli Observatory and Earthquake Research Institute Regional Earthquake-Tsunami Monitoring Center were used in this study. The maximum S-wave and maximum P-wave amplitude ratio of vertical component velocity seismograms, power ratio (Complexity) and total signal duration of the waveform were calculated. Earthquakes and quarry blasts were discriminated using the linear discriminate function (LDF) and back propagation feed forward neural networks, an artificial neural network (ANN) learning algorithm, taking the determination coefficient and variance account values between these parameters into consideration. Eighty-one (54%) of the total 150 seismic events studied were determined to be earthquakes, and sixty-nine (46%) of them were determined to be quarry blasts. The LDF and ANNs methods were applied to the data in Edirne and its vicinity using a pair of parameters and were compared to each other for the first time. The accuracy of the methods are 95% and 99% for LDF and ANNs, respectively.

ARTALAN SİSMİK GÜRÜLTÜ VERİLERİNDEN ELDE EDİLEN GREEN FONKSİYONLARININ GEÇERLİLİĞİNİN ADANA HAVZASINDAKİ ANDIRIN DEPREMİ İLE DOĞRULANMASI

The vertical component continuous data recorded by the national seismological networks (Kandilli Observatory and Earthquake Research Institute (KOERI) of Bosporus University and Earthquake Research Department (ERD) of Disaster and Emergency Management Presidency of Turkey) in the Adana Basin (Southeastern Turkey) are used to retrieve the Green’s functions between two stations. The noise data were cut into 1-hour segments, scanned for the gaps caused by transmission drop-outs, preprocessed by removing the trend, mean and instrument response, down sampled to 10sps and low-pass filtered at 50s. Then the hourly cross-correlations are computed and stacked and the Green’s functions between two stations are retrieved. To validate the retrieved Green’s functions, the Andirin earthquake of magnitude 5 occurred on 22.07.2012 near the station Andirin (ANDN) is used. By using the ANDN station as the virtual source, the Green’s functions at KARA, KMRS, KIZK, MERS and YAYL stations are compared with the real earthquake seismograms. The agreement between the earthquake seismograms and the retrieved Green’s functions suggests that the Rayleigh wave group velocities can reliably be estimated for the region by using ambient noise data.

Investigation of the Hemispheric Asymmetry in Solar Flare Index During Solar Cycle 21 – 24 from the Kandilli Observatory

The hemispheric asymmetry of the solar-flare index during 1976 – 2018 from the Kandilli Observatory is studied in this investigation. The temporal duration covers Solar Cycles 21 – 23 and almost the whole of Solar Cycle 24. Different methodologies, such as cross-correlation analysis, rescaled-range analysis, empirical mode decomposition, and date-compensated discrete Fourier transform, have been used on the hemispheric solar-flare index as well as on absolute asymmetry data to study various inherent characteristics. We observed that: i) the temporal characteristics in the northern and southern hemispheres are different during the progression of a solar cycle; ii) the T-test indicates that Solar Cycles 21 and 23 do not have any dominant hemispheric effect, whereas Solar Cycle 22 and 24 have South-dominated hemispheric characteristics; iii) the southern hemisphere is leading by ten, three, and one months during Solar Cycles 21, 22, and 24, respectively, and for Solar Cycle 23 the hemispheres are in phase; iv) anti-persistence as well as short memory-dependent characteristics are present in both the hemispheric solar-flare index and the absolute asymmetry data; v) all of the time-series data have well-known periods of 11 years and 27 days as well as short-term periods around 7 days and 14 days. Apart from those, several mid-term periodicities such as the Rieger periodicity and quasi-biennial oscillations (QBOs) are also found in both hemispheric solar-flare index as well as absolute asymmetry index data; vi) the Waldmeier effect is also validated using solar-flare-index data. These results will enrich our knowledge about the distribution of hemispheric asymmetry in solar-flare-index data and may reveal some valuable points about asymmetry behaviors.