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Crustal structure at the western end of the North Anatolian Fault Zone from deep seismic sounding (2006)

Karahan, A. E. ; Berckhemer, H. ; Baier, B.

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Publication Date: 2019-11-04

Description: The first deep seismic sounding experiment in Northwestern Anatolia was carried out in October 1991 as part of the "German - Turkish Project on Earthquake Prediction Research" in the Mudurnu area of the North Anatolian Fault Zone. The experiment was a joint enterprise by the Institute of Meteorology and Geophysics of Frankfurt University, the Earthquake Research Institute (ERI) in Ankara, and the Turkish Oil Company (TPAO). Two orthogonal profiles, each 120 km in length with a crossing point near Akyazi, were covered in succession by 30 short period tape recording seismograph stations with 2 km station spacing. 12 shots, with charge sizes between 100 and 250 kg, were fired and 342 seismograms out of 360 were used for evaluation. By coincidence an M b = 4.5 earthquake located below Imroz Island was also recorded and provided additional information on Moho and the sub-Moho velocity. A ray tracing method orginally developed by Weber (1986) was used for travel time inversion. From a compilation of all data two generalized crustal models were derived, one with velocity gradients within the layers and one with constant layer velocities. The latter consists of a sediment cover of about 2 km with V p » 3.6 km/s, an upper crystalline crust down to 13 km with V p » 5.9 km/s, a middle crust down to 25 km depth with V p » 6.5 km/s, a lower crust down to 39 km Moho depth with V p » 7.0 km/s and V p » 8.05 km/s below the Moho. The structure of the individual profiles differs slightly. The thickest sediment cover is reached in the Izmit-Sapanca-trough and in the Akyazi basin. Of particular interest is a step of about 4 km in the lower crust near Lake Sapanca and probably an even larger one in the Moho (derived from the Imroz earthquake data). After the catastrophic earthquake of Izmit on 17 August 1999 this significant heterogeneity in crustal structure appears in a new light with regard to the possible cause of the Izmit earthquake. Heterogeneities in structure are frequently also heterogeneities in strength and stress that impede or even lock rupture. The Izmit earthquake is discussed in relation to a large stepover or jog at the North Anatolian Fault.

Description: JCR Journal

Description: open

Keywords: north Anatolian fault zone ; crustal structure ; deep seismic sounding ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology

Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Type: article

Format: 7542902 bytes

Format: application/pdf

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Accompanying seismic refraction investigations along the profile DEKORP 2-North (1990)

Giese, P. ; Ibbeken, S. ; Baier, B. ; [et al.]

Springer

International journal of earth sciences 79 (1990), S. 567-579

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ISSN: 1437-3262

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Description / Table of Contents: Abstract Seismic refraction measurements were carried out along the DEKORP 2-N reflection line. Traveltime data have been inverted to velocity-depth distributions using x-t-inversion- und ray-tracing-methods. The velocity-model shows alternating layers of high and low velocity. High-velocity values range from 6.0 to 6.6 km/s in the upper crust and from 70 to 8.2 km/s in the lower crust. In low-velocity zones velocities do not exceed 6.25 km/s. The crust/mantle boundary lies in about 28–30 km depth. Correlations exist between the velocity-model of refraction seismics and the line drawing section of reflection seismics.

Abstract: Résumé Des mesures en sismique-réfraction ont été effectuées le long du profil de sismique réflexion DEKORP 2-N. On a réalisé une inversion des temps de propagation en distribution vitesse/profondeur par les méthodes de l'inversion x-t et du traçage de raie. Le modèle des vitesses fait apparaître des couches alternées à grandes et faibles vitesses. Les grandes vitesses sont de 6,0 à 6,6 km/sec dans la croûte supérieure et de 7,0 à 8,2 km/sec dans la croûte inférieure. Dans les zones à faible vitesse, celle-ci n'excède pas 6,25 km/sec. La profondeur du contact croûte/manteau est d'environ 28 à 30 km. Il existe une correspondance entre le modèle des vitesses de la sismique-réfraction et l'image fournie par la sismique-réflexion.

Notes: Zusammenfassung Entlang dem tiefenseismischen Reflexionsprofil DEKORP 2-Nord wurden seismische Refraktionsmessungen durchgeführt. Die Laufzeitdaten wurden mit Hilfe von x-t-Inversions- und Ray-Tracing-Verfahren in Geschwindigkeits-Tiefen-Verteilungen transformiert. Es treten alternierende Hoch- und Niedriggeschwindigkeitszonen auf. In der oberen Kruste treten hohe Geschwindigkeitswerte im Bereich von 6,0 bis 6,6 km/s auf und in der unteren Kruste Werte von 7,0 bis 8,2 km/s. Die Geschwindigkeitswerte in Niedriggeschwindigkeitszonen überschreiten 6,25 km/s nicht. Die Grenze zwischen Erdkruste und Erdmantel liegt in einer Tiefe von etwa 28 bis 30 km. Es bestehen Übereinstimmungen zwischen dem Geschwindigkeitsmodell der Refraktionsseismik und der Struktur der reflexionsseismischen Sektion.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01879202

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