Tolga Gönenç

A microgravity model for the city of İzmir (Western Anatolia) and its tectonic implementations

Western Anatolia has an extensional tectonic regime and the characteristics of the deformation in the continental crust observed in Aegean Region have a very complex structure. In our study area, the İzmir city, Turkey, which is located within this active region, the general geological setting is also rather complex. This first microgravity study in İzmir and its surroundings is related to the determination of active fault zones. It was conducted in the south of İzmir, with the aim to investigate this complex structure in detail through microgravity data collected from six profiles throughout the survey area. The variation in Bouguer values was profoundly investigated along Profile P1 in N-S direction that was delineated to intersect all the tectonic elements. For this reason, Profile P1 was modeled in this study as 2D. As a result, the created gravity model was investigated together with geology, earthquake focal depths, and isostasy.

Investigation of the relationship between ground and engineering bedrock at northern part of the Gulf of İzmir by borehole data supported geophysical works

Loss of life and property that may occur as a result of a possible earthquake can be reduced by earthquake resistant building designs. In order to investigate possible ground motion amplification in earthquake resistant building design, relationship between the ground and engineering bedrock must be ensured. In order to provide this relation, structure, basic characteristics, and thickness of the ground are investigated. In this context, calculating ground transfer function, obtaining horizontal earthquake acceleration changes, calculating Vs values and defining the engineering bedrock are necessary. In this study, Menemen plain, the nothern part of Izmir metropolitan located in active earthquake zone and its immediate vicinity have been examined to define the structure, ground, engineering and bedrock relation. In this context, Menemen plain has been investigated by geophysical methods, which are supported with borehole data (microtremor, MASW – multichannel analysis of surface waves, microgravity measurements, and vertical electrical sounding–VES). Microtremor method was conducted at 377 points in average in the investigation area to define fundamental period and empirical transfer function; after that in order to create basin model and to define the shallow subsurface geometry, microgravity measurements were carried out by using Scintrex CG-5. Also, MASW measurements were carried out in approximately 277 profiles and Schlumberger VES measurements were conducted at approximately 7 points in the investigation area. The existence of a linear relation between H/V peak period values obtained by microtremor measurements and ground thickness in the investigation area is also supported by geothermal drilling logs (depth of 600 m) with microgravity survey. Also, in some parts of the investigation area, it was observed that high S velocity (Vs) values affected H/V peak period values in sections of the ground close to the surface and there was an inversely correlated relation between this ground thickness and peak period values. This event occurring in shallow depths is supported by both VES sections and 2nd order vertical gravity derivative. As a result, depth of the engineering bedrock was obtained between 200 and 700 m and this unit was proposed as Bornova Melange for the investigation area in the scope of the works carried out. Also, it is observed that the area from ground to the engineering bedrock consists of four different layers which were defined by individual S velocities and densities. According to all results, characterictics of the shallow subsurface show that there is a high heterogeneity. Therefore, according to Eurocode8 (EC8 2004) regulations, soil characteristic of the Menemen plain and its vicinity are in the S1–S2 soil class.

Investigation of vertical mass changes in the south of Izmir (Turkey) by monitoring microgravity and GPS/GNSS methods

The monitoring of gravity changes in a region enables the investigation of regional structural elements depending upon the changes in load compensation. This method, preferred in recent years, has yielded good results from different parts of the world for determination of the deformation at fields. With the addition of GPS/GNSS monitoring to microgravity studies, the mass changes within the crust in vertical directional movements of a region can be estimated. During GPS/GNSS monitoring and microgravity studies, it was found that the behaviour of vertical directions of Izmir and the surrounding areas, indicate an active tectonic regime and high seismic activity, especially since 2000. As a result, regions considered to have a mass change in vertical direction were determined by 3-year measurements and it was found that they were consistently highly seismic.

The Investigation of Hot Spots in Western Anatolia by Geophysical and Mining Approaches

Abstract In the first part of this article, a short definition of geothermal energy is made and geothermal fields are classified according to their enthalpies. In the second part, general uses of geothermal energy and also the geothermal potential of Turkey and especially of western Anatolia are mentioned. Then, the general geology of the study area moving from three example geothermal fields is depicted and supported by lithological columns. The tectonic structure of our study area, western Anatolia, is profoundly explained and the presence of geothermal fields in this area is backed up by geophysical findings in detail in the final section.

The Stress/Strain Analysis of Kinematic Structure at Gülbahçe Fault and Uzunkuyu Intrusive (İzmir, Turkey)

Abstractİzmir and its surroundings constitute an important tectonic region for the control of the Western Anatolian region. The study area is located in the western part of İzmir city and inside of Karaburun Peninsula. In the study area and its surroundings, a great amount of earthquakes occurred in both land and sea in recent years. Hence, the kinematic structures of Gülbahçe fault and Uzunkuyu intrusive were examined within this study. As a first step, the mechanism and the velocities of these faults were identified using the GNSS data. Then, a stress and strain analysis of the region was performed for different depths using Coulomb software. In this study, the strain changes on vertical direction were evaluated and compared with the changes of observed gravity anomalies for the first time for the study area as distinct from the previous studies. From this integrated analysis, we retrieved the kinematic parameters and movement mechanisms of Gülbahçe fault and Uzunkuyu intrusive and defined the regional stresses, the strain changes and the kinematic models of them.

VERTICAL AND HORIZANTAL ANALYSIS OF CRUSTAL STRUCTURE IN EASTERN ANATOLIA REGION

The tectonic regime of Eastern Anatolia is determined by Arabian-Eurasian continent- continent convergence and the mechanism occurred with the convergence. North Anatolian Fault Zone (NAFZ), Eastern Anatolian Fault Zone (EAFZ), North Eastern Anatolian Faults and Bitlis Zagros Suture Zone are formed by this convergence, represent the characteristic of lithospheric structure of the region. In the scope of this study, the gravity anomalies of Eastern Anatolia were used for investigating the lithospheric structure. Firstly, second order trend analyses were applied to gravity data for examining the characteristic of the anomaly. Later, the vertical and horizontal derivatives methods were applied to the same data. Generally, the purpose of the applying derivative methods is determining the vertical and horizontal borders of the structure. Therefore, this method gives the opinion about the characteristic of the lithospheric structure of the study region. According to the results of derivative methods, the structure transitions were increased rather especially with Bitlis Zagros Suture Zone. At the last step, the gravity studies were evaluated together with the seismic activity of the region. Consequently, the geodynamical structure of the region is examined with the previous studies done in the region.

Using GPS data together with geophysical data: A Case study from a seismically active region, Izmir

Essential developments on computer systems and space technologies have given rise to GPS (Global Positioning System) enter into our daily lives. In 1970s, with the advent and rapid development of U.S. Global Positioning System (GPS) a new era in geodesy and geophysics has started. After 1980s GPS has been used for monitoring crustal movements in the world. Likewise, since 1989, GPS data has been and are still being used for earthquake prediction purposes in Turkey. Consequently, in recent years, GPS studies as well as the other geophysical studies have gained importance in tectonically active regions like Turkey. GPS data obtained from episodic observations and/or CORS(Continuously Operating Reference Stations) network provide detailed information that help researchers identify changes which cause earthquakes. Because earthquakes occur as a result of movement of the earths crust, today, seismologists and geophysicists are able to measure such movements with high precision with the use of GPS data. In this context, a case study in Izmir and its surrounding, which has active seismicity and tectonism and is located within the N-S trending extensional system in Western Anatolia Region, was performed under the scope of The Scientific and Technological Research Council of Turkey (TÜBİTAK-108Y285) project. Within the framework of this project, GPS observations were performed in Izmir and its surrounding. Then, the GPS velocity vectors were evaluated with microgravity and seismological data. Consequently, in this study, the literature work about the usage of GPS methods in geophysical studies and the information regarding the studies are presented.