Browsing by Author "Alkan, H."

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Multiple Parameter Analysis for Assessing and Forecasting Earthquake Hazards in the Lake Van Region, Turkey
(Nature Research Centre, 2023) Öztürk, S.; Alkan, H.
A detailed spatial-temporal analysis of the seismic activity in and around the Lake Van region was performed using several seismotectonic parameters such as b-value, Z-value, relative intensity (RI), pattern informatics (PI), and Coulomb stress changes. Correlations between these parameters were analyzed to esti-mate and forecast potential seismic hazards in the Lake Van region. Particular attention was paid to the parts of the study region that exhibited smaller b-values, higher Z-values, and high-stress changes at the beginning of 2022 and to the locations of earthquake hotspots determined from the composite earthquake forecast map for 2022–2032, i.e., Muradiye, Çaldıran, Özalp, Erçek, Van city center and Gevaş covering the faults of Çaldıran, Yeniköşk, Erciş, Malazgirt and the fault zones of Saray and Van. To provide more accurate interpretations regarding potential earthquake occurrences in the near future, the seismotectonic parameters analyzed in the scope of this study were compared with the corresponding seismological, geological, geodetical, and geochemical variables reported in the literature. This comparison showed that, firstly, our results are consistent with those reported in previous studies, and, secondly, all these variables should be interpreted in combination to correctly assess strong earthquake hazards. Furthermore, this type of multiple-parameter analysis may be important for the description of seismic, tectonic, and structural characteristics of the nature of the crust. Our findings show that almost all seismotectonic parameters indicative of anomaly regions, i.e., lower b-values, higher Z-values, high-stress distribution, and hotspots, were recorded in the same parts of the study region. Thus, the anomaly regions detected at the beginning of 2019 and between 2022 and 2032 may be considered to be potential zones of future great earthquakes. To summarize, the correlations among these variables may provide accurate information for assessing and forecasting earthquake hazards in this region. © Baltica 2023.
P-And S-Receiver Functions Analysis and Joint Inversion: Lithospheric Structure Below Erzurum Vicinity
(Hacettepe Universitesi Yerbilmleri, 2023) Alkan, H.
The receiver function technique is frequently used by geophysicists to determine discontinuities and to suppose the layer thicknesses in the crust and upper mantle. A receiver function is a time series in which phases are converted from P to S or S to P. In this study, the time-domain deconvolution method, depth and slowness stack, and the joint inversion algorithm are performed. In the aim of the study, teleseismic data is selected for the recorded at SENK and ECAT stations located in Erzurum city. P-and S-wave velocities, and Vp/Vs ratios are calculated for the lithospheric structure beneath these stations. The results of this study are generally consistent with previous receiver function findings applied in the study region. © 2023, Hacettepe Universitesi Yerbilmleri. All rights reserved.
A Preliminar P and S-Wave Receiver Functions Study at Ktut Station (Trabzon, Turkey)
(European Association of Geoscientists and Engineers, EAGE, 2017) Alkan, H.; Çinar, H.
To better understand the deep structure of the Eastern Pontides orogenic belt (NE Turkey), we have just analyzed the teleseismic-records of the KTUT station as an initial study. For this purpose, P and S Receiver Functions are calculated, and then inverted jointly together with teleseismic P and S traveltime residuals. The inversion is performed using a simulated annealing technique. No high-quality signal is observed at the KTUT station for the Ps converted phase from P410s and P660s km discontinuity. An early arrival is observed at this station for P410s which is ~0.5 s than the IASP91 global model. The crust has a thickness of about 34 km, and the high-S-velocity mantle lid is beneath the crust at a depth of about 65 km. The velocities of Vs and Vp in the crust are close to Vs= ~3.61 km/s and Vp= ~6.37 km/s, respectively. The S wave velocity decreases to ~4.22 km/s at the low-S-velocity zone beneath the crust, and it reaches to ~4.65 km/s at upper mantle. Consequently, the crust and upper mantle thicknesses derived from the receiver functions analyses are in good agreement with results from other studies. © 2017 European Association of Geoscientists and Engineers EAGE. All Rights Reserved.
A Statistical Analysis and Evaluation on the Earthquake Forecasting and Hazard for Lake Van and Its Adjacent Area (Türkiye)
(Afet ve Acil Durum Yonetimi Baskanligi (AFAD), 2022) Ozturk, S.; Alkan, H.
In this study, current earthquake hazard is tried to present and earthquake forecasting is made for Lake Van and its adjacent area for the next five years. For this purpose, a statistical analysis is achieved with the concomitant use of the b-value, Z-value, relative intensity (RI) and pattern informatics (PI) data. In addition, for the earthquake forecasting in the intermediate term and hazard, a comprehensive discussion is made with the studies analyzing the different seismological and geophysical variables in literature. The relations between these parameters reveal more accurate and reliable approaches. Consequently, at the beginning of 2022, particularly the areas having small b-value and large Z-value with the hotspots (possible earthquake areas) between 2022 and 2027 from the combined forecast map are determined in and around Muradiye, Çaldıran, Özalp, Van city centre and Gevaş including Çaldıran, Yeniköşk, Erciş and Malazgirt faults with Saray and Van Fault zones. © 2022 ARSMB-KVBMG. All rights reserved.
Stress Accumulation on the Karlıova (Bingöl) Triple Junction After Two Big Earthquakes (Pazarcık-Ekinözü) in Turkey in 2023
(Ist Nazionale Di Oceanografia E Di Geofisica, 2025) Bektas, O.; Pirti, A.; Alkan, H.; Yucel, M. A.; Buyuksarac, A.
Active fault zones primarily influence earthquakes in the Karl & imath;ova (Bing & ouml;l) region. The mentioned region is in Turkey's first and second seismic hazard zones; however, it also includes certain areas in the third and fourth seismic hazard zones. In this study, we investigated the earthquake activities using data collected from various global navigation satellite system (GNSS) surveys of continuously operating reference stations in Turkey (CORS-TR). We also analysed the Coulomb stress change caused by the 15 local earthquakes surrounding the Karl & imath;ova Triple Junction. Additionally, we investigated the relationship between Coulomb stress change and horizontal displacements from GNSS survey results, focusing on horizontal displacement vectors. Besides, gravity data were used to infer the fault geometries and shallow crustal structures. The largest horizontal movement was observed at the BIN1 station, the intersection point of the North Anatolian Fault Zone (NAFZ) and the East Anatolian Fault Zone (EAFZ). At the CORS-TR point on the Karl & imath;ova segment of the EAFZ, the horizontal displacement was calculated to be approximately 10.1 cm in the north-eastern direction. The observations of Coulomb stress change reveal that positive stress variations were observed in the NW-SE and SW-NE directions along the main fault line at a depth of approximately 30 km, in accordance with the tilt transformation of gravity anomalies.
Teleseismic Receiver Functions and Gutenberg-Richter Bvalue Distributions Around the Lake Van Region (Eastern Turkey)
(EAGE Publishing BV, 2019) Alkan, H.; Çinar, H.; Bayrak, E.
This study will supply an overview of crust and upper mantle structure beneath the Lake Van region based on the Receiver Function analyses of P- and S- waves using the teleseismic data set taken from the European Integrated Data Archive. All inversion results will depict the present day tectonics of the Lake Van region. Also, spatial variations of the b-values are calculated by using data covers all earthquakes occurred between 1900-2017. The b-values will inform us about the compatibility between the seismic regime and seismic velocity for the depth from near surface to 30 km. Copyright © Congress of Balkan Geophysical Society, BGS 2019. All rights reserved.