Earthquake Research Institute Research Articles

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.

Detection of Deep Low‐Frequency Tremors From Continuous Paper Records at a Station in Southwest Japan About 50 Years Ago Based on Convolutional Neural Network

AbstractSince deep low‐frequency tremors are considered to be associated with large earthquakes that occur adjacently on the same subducting plate interface, it is important to investigate tremors that occurred before the establishment of modern seismograph networks such as the High Sensitivity Seismograph Network (Hi‐net). We propose a deep‐learning solution to detect evidence of tremors in scanned images of paper seismogram records from over 50 years ago. In this study, we fine‐tuned a convolutional neural network (CNN) based on the Residual Network, which was pre‐trained using images of synthetic waveforms from our previous study, using a data set comprised of images generated from real seismic data recorded digitally by Hi‐net to facilitate a supervised analysis. The fine‐tuned CNN was able to predict the presence or absence of tremors in the Hi‐net images with an accuracy of 98.64%. Gradient‐weighted Class Activation Mapping heatmaps created to visualize model predictions indicated that the CNN's ability to detect tremors is not degraded by the presence of teleseisms. Once validated using the Hi‐net images, the CNN was applied to paper seismograms recorded from 1966 to 1977 at the Kumano observatory in southwest Japan, operated by Earthquake Research Institute, The University of Tokyo. The CNN showed potential for detecting tremors in scanned images of paper seismogram records from the past, facilitating downstream tasks such as the creation of new tremor catalogs. However, further training using an augmented data set to control for variables such as inconsistent plotting pen thickness is required to develop a universally applicable model.

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.

Performance of Seismic Observation by Distributed Acoustic Sensing Technology Using a Seafloor Cable Off Sanriku, Japan

Recently, the distributed acoustic sensing (DAS) measurement, which utilizes an optical fiber itself as a sensor, becomes popular for various fields and is being applied to seismic observations. The shortest spatial sampling of DAS observations reaches a few meters, and the total measurement distance becomes greater than 50 km. A high temporal sampling rate is achieved. Due to these characteristics, a DAS measurement allows for a dense seismic observation as a linear array. Applying a DAS measurement to the seafloor cable is advantageous because the quantity of data can be significantly increased in a marine area. A seafloor seismic tsunami observation cable system using an optical fiber for data transmission was deployed off Sanriku by the Earthquake Research Institute, the University of Tokyo in 1996. This seafloor cable observation system has spare fibers for extension. Beginning in February 2019, we made several DAS observations using the spare fibers of the seafloor system. Consequently, many earthquakes were recorded. Small earthquakes with a magnitude of 1.8 occurring near the cable system were recorded by the DAS system. The arrivals of P- and S-waves of the earthquake with a magnitude of 3 were clearly seen using the phase data from the DAS measurement. In addition, a teleseismic event with an epicentral distance of approximately 2,300 km and a magnitude of 6.6 was clearly observed. Because there are conventional seismometers in the Sanriku cable system, we compared records from the DAS measurement with those from the seismometer. The DAS records and the data by the seismometer showed a high coherency. The noise levels of the DAS measurement were evaluated, and there was little temporal variation of the noise levels. A spatial variation of ambient seismic noises was revealed using a spatially high-density observation with a long distance. In November 2020, a seismic survey using the DAS system and airguns was carried out, and the DAS system clearly recorded signals from the airguns. We also compared these data from the DAS system with that of the seismometer. Both records had the same characteristics, although P-wave arrivals on the DAS records have smaller amplitude.

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.

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.

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.

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.

Core-to-Core Collaborative Research Between Earthquake Research Institute, The University of Tokyo and Disaster Prevention Research Institute, Kyoto University During FY2014 to FY2018

The research program titled “Earthquake and Volcano Hazards Observation and Research Program” was started in fiscal year (FY) 2014 as a new five-year project authorized and funded by the Council for Science and Technology of the Ministry of Education, Culture, Sports, Science and Technology. It included a new format of collaborative research called, “Core-to-Core Collaborative Research between Earthquake Research Institute, The University of Tokyo and Disaster Prevention Research Institute, Kyoto University.” In this format, two types of research, “Participation Type Research” and “Subject Proposal Type Research” were conducted from FY2015. A preliminary study was performed in FY2015 for “Integrated Research” of “Participation Type Research,” which developed a framework for seismic risk evaluation at prefectural offices of Osaka and Kochi for an earthquake occurring along the Nankai Trough, considering the epistemic uncertainty. The secondary study was performed from FY2016 through to FY2018, wherein the methodology for the seismic risk evaluation was improved on three aspects: i.e., revision in ground motion prediction models considering the saturation effect, revision in loss models in terms of the fatalities as well as the direct losses of buildings, and extension of target sites to the whole of Osaka and Kochi prefectures. The results suggest that the epistemic uncertainty in the ground motion prediction models is most sensitive to the overall uncertainty of seismic risk. Along with “Integrated Research,” a total of 14 “Research on Specific Topics” related to time-dependent risk analysis, economical risk evaluation, source characterization, structural damage estimation models, ground motion estimation models, soil amplification models, and disaster prevention planning considering the uncertainty of risk assessment, were studied during this period in order to improve the risk assessment studies for “Integrated Research.” With respect to “Subject Proposal Type Research,” a total of 27 individual research themes focused on research to understand hazards/risks by earthquakes and volcanic eruptions and to mitigate disasters by them.

Two Earthquake Sequences Nearly a Century Apart Reveal a Conjugate Seismogenic System in Central Taiwan

Abstract Seismically active central Taiwan is considered part of an orogenic wedge with low-angle east-dipping active faults above a detachment surface and an active mountain-building process later. In 2013, two moderate reverse-faulting earthquakes of magnitudes ML 6.2 and 6.5 occurred in Nantou. They brought to mind the historically damaging sequence of four earthquakes in the same area that claimed a total of 71 lives in 1916. The 2013 earthquake sequence provides a good opportunity to study the 1916 sequence. We compared the historical Omori record of the main event in the 1916 sequence, discovered in the Seismogram Archives at the Earthquake Research Institute, University of Tokyo, and the corresponding simulated Omori records of the 2013 events. Our comparison shows significant similarity among the earthquakes, although they are separated by nearly 100 yr. To understand the seismogenic structure associated with these earthquake sequences, we further studied the source rupture properties of earthquakes in this region since 1999 using local broadband records to determine the rupture fault planes. Results show that all events have similar focal mechanisms with one low-angle east-dipping and another high-angle west-dipping nodal planes. Rupture plane determination indicates that whereas events at shallow depths (&amp;lt;20 km) ruptured on the low-angle east-dipping plane, events at greater depths (&amp;gt;20 km) slipped on the high-angle west-dipping plane in a conjugate fault system. The comparison also suggests that the 1916 sequence occurred on the low-angle east-dipping plane of this conjugate fault system in the orogenic wedge as part of a mountain-building process. Given the active mountain-building process in central Taiwan, occurrences of this type of earthquake must be addressed in seismic hazard mitigation efforts.

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 Database of Digitized and Analog Seismograms of Historical Earthquakes in Japan

AbstractSeismic and tsunami instrumental observations by seismographs and tide gauges began in Japan in 1875; hence, many analog records of earthquakes and tsunamis are stored at various universities and institutions throughout the country. Re-examination of historical records using modern waveform analysis methods, high-performance computing, and current knowledge on seismic velocity structure is expected to produce new results and interpretations of the mechanism of large earthquakes and tsunamis, leading to improved seismic disaster mitigation practices. However, such work requires extensive effort and skills for the digitization of the analog waveforms recorded on papers. To conveniently use the analog seismograms, we currently construct a database of digitized historical records and seismogram image copies of major earthquakes that occurred in Japan (e.g., the 1923 Kanto, 1944 Tonankai, and 1946 Nankai earthquakes). The data can be searched in this database by event, station, and seismograph names. Users can obtain the instrumental response and station information, if available, in addition to the digitized data. We plan to open this database to the public in a few years via the National Museum of Nature and Science and the Earthquake Research Institute of the University of Tokyo. The database on the museum website will be fundamental for outreach activity of seismology for the general public, and the information contained in the database will be useful in various fields such as seismology or earthquake engineering.