Erhan Altunel

The Surface Rupture and Slip Distribution of the 17 August 1999 İzmit Earthquake (M 7.4), North Anatolian Fault

The 17 August 1999 Izmit earthquake occurred on the northern strand of the North Anatolian fault zone. The earthquake is associated with a 145-km-long surface rupture that extends from southwest of Duzce in the east to west of Hersek delta in the west. Detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step-overs; herein named the Hersek, Karamursel-Golcuk, Izmit-Sapanca Lake, Sapanca-Akyazi, and Karadere segments from west to east, respectively. The Hersek segment, which cuts the tip of a large delta plain in the western end of the rupture zone, has an orientation of N80°. The N70°-80°E-trending Karamursel-Golcuk segment extends along the linear southern coasts of the Izmit Gulf between Karamursel and Golcuk and produced the 470-cm maximum displacement in Golcuk. The northwest-southeast-striking Golcuk normal fault between the Karamursel-Golcuk and Izmit-Sapanca segments has 2.3-m maximum vertical displacement. The maximum dextral offset along the Izmit-Sapanca Lake segment was measured to be about 3.5 m, and its trend varies between N80°E and east-west. The Sapanca-Akyazi segment trends N75°-85°W and expresses a maximum displacement of 5.2 m. The Karadere segment trends N65°E and produced up to 1.5-m maximum displacement. The Karadere and Sapanca-Akyazi segments form fan-shape or splaying ruptures near their eastern ends where the displacement also diminished.

Travitonics: using travertines in active fault studies ☆

Abstract Late Quaternary travertines deposited from hot springs can reveal much about the neotectonic attributes and histories of structures. On the basis of field studies in the Aegean region (Turkey and Greece), the northern Apennines (Italy) and the Basin and Range province (USA) we conclude that the following relationships are of predictive value: (i) travertine deposits are preferentially located along fracture traces, either immediately above extensional fissures or in the hanging walls of normal faults; (ii) the locations of many travertine fissure-ridge deposits coincide with step-over zones (relay ramps) between fault segments; networks of intersecting tensional fissures reflecting the complex strains experienced in such settings are probably responsible for enhancing hydrothermal flow; (iii) the morphology of travertine deposits overlying extensional fissures is controlled by the rheology of the underlying materials; tufa cones (towers, pinnacles) form on former and present lake floors where fissures underlie unconsolidated sediments, whereas fissure-ridges develop where fissures cut bedrocks at the surface; (iv) fissure-ridges comprise outwardly dipping bedded travertine flanking a central tensional fissure filled by vertically banded travertines; fissures can be used to infer local stretching directions; (v) where there are travertines datable by the U-series method it is possible to calculate time-averaged dilation and lateral propagation rates for individual fissures; (vi) most fissures cutting fissure-ridges comprise self-similar angular segments with fractal dimensions in the range 1.00–1.12, the properties of bedded travertine combined with stress perturbations at fissure tips probably being responsible for such similar fractal dimensions being inferred from such a wide range of locations. Fissures gradually increasing in width with depth are products of continuous fracture dilation in contrast to those that form during episodic dilation which display stepped increases of width with depth; (vii) travertine deposited from springs along fault zones accumulate in terraced-mounds sited down slope of the spring line; (viii) many post-depositional fractures cutting travertine deposits are locally oriented at right angles to deposit margins; and (ix) systematic joints in travertines are restricted to those parts of eroded sheet deposits that have been exhumed.

Surface Rupture and Slip Distribution of the 12 November 1999 Düzce Earthquake (M 7.1), North Anatolian Fault, Bolu, Turkey

The 12 November 1999 earthquake ( M 7.1) occurred on the Duzce fault, a splay of the North Anatolian fault in the Bolu basin approximately three months after the 17 August 1999 ( M 7.4) earthquake. The surface rupture was 40 km long, and the maximum right-lateral offset was 500 ± 5 cm, averaging 300 cm. The 9 km of the westernmost part of the rupture along the southern margin of the Eften Lake had a 350-cm maximum vertical displacement (normal faulting), some of which was already ruptured during the 17 August 1999 event with few tens of centimeters. The surface rupture has a generally simple narrow deformation zone of 0.5-5 m, however, in some places, it widens to 50 m. Transtensional and transpressional structures were observed within releasing and restraining step-over areas respectively. The larger dextral offsets on some streams indicate previous events. The dextral slip measurements along the rupture reflect a symmetric distribution. The eastern connection of this rupture zone with the main trace of North Anatolian fault remains unclear because the Bakacak and Elmalik fault, which are connecting faults, had no surface rupture. Manuscript received 14 November 2000.

Determination of horizontal extension from fissure-ridge travertines: a case study from the Denizli Basin, southwestern Turkey

Travertine deposits reflect some aspects of the regional tectonics because of the close association between travertine deposits and active fractures, that later of which provide conduits along which travertine-depositing waters may rise. Fissure-ridge travertines form above extensional fissures which are located in the hanging walls of normal faults, in step-over zones between fault segments, or in active or recently active) volcanic provinces. Numerous active and inactive fissure-ridge travertines are located in the hanging walls of normal faults in the Denizli Basin. A typical fissure-ridge comprises a central fissure along its long axis and flanking bedded travertines dipping away from the fissure. Central fissures of travertine ridges have been dilating since the initiation of the fissures. Samples from both the margins and centres of banded travertine deposits were dated by Th/U methods in order to determine dilation rates. Individual fissures have been dilating at average rates of between 0.008 and 0.1 mm yr–1 during travertine deposition, and ~ 0.001 and 0.007 mm yr–1 after cessation of travertine deposition. There is a noticable decrease in dilation rate from west to east in the Denizli Basin, and this decrease in dilation rate may be related to decrease in overall extension in southwest Turkey, which decreases eastward.

Surface Rupture and Slip Distribution along the Karadere Segment of the 17 August 1999 İzmit and the Western Section of the 12 November 1999 Düzce, Turkey, Earthquakes

On 17 August 1999 the Mw 7.5 I zmit, Turkey, earthquake produced surface rupture in excess of 120 km, and perhaps as much as 200 km, with up to 5 m of dextral slip, along a western portion of the North Anatolian fault zone. The 12 November 1999 Mw 7.1 Duzce, Turkey, earthquake produced a 40-km-long sur- face rupture, including 9 km of rupture overlap with the eastern end of the August event. Our mapping focused on the 40-km-long Karadere rupture segment, the east- ernmost segment of the August event, as well as on the western 20 km of the No- vember rupture. Maximum dextral slip along the Karadere segment is approximately 1.5 m, and the average slip on this segment is close to 1 m. Although slip along the Karadere segment is considerably less than that on segments to the west, this segment is of particular interest for three reasons: (1) the western boundary of the Karadere segment is defined by the most striking structural discontinuity along the entire Au- gust surface rupture (i.e., a 5-km-wide zone of no surface rupture, as well as a 25 change in trend from E-W to ENE), and such a discontinuity may have important implications for rupture dynamics; (2) surface rupture terminates at the east end of the Karadere rupture segment at a 1.5- to 3-km-wide extensional step-over at Eften Lake; and (3) the 12 November 1999 Duzce earthquake reruptured the easternmost 9 km of the Karadere segment, raising interesting questions about rupture dynamics and interactions between events on adjacent fault segments. The details of the 17 August 1999 and l2 November 1999 surface rupture traces suggest that rupture may have partially propagated across the Eften Lake extensional step-over, although this step-over seems to have acted as an effective barrier to rupture propagation.

Geological and archaeological evidence for post– Roman earthquake surface faulting at Cibyra, SW Turkey

Abstract The NE–SW-trending Burdur–Fethiye fault zone is one of the major active fault zones of southwestern Turkey and the ancient city of Cibyra is located on this zone. Segments of the Burdur–Fethiye fault zone have ruptured in the historical period and during the 20th century. A detailed investigation in the ancient city of Cibyra showed the presence of faults sinistrally offset sitting rows of the stadium up to 50 cm. In addition, there are broken corners of blocks, collapsed walls, broken columns, and tilted and toppled blocks in existing major buildings in the city centre. Field observations showed that fractures and associated damage at Cibyra were produced by a post-Roman earthquake, possibly during the 417-A.D.-earthquake which had an intensity of 9 on the MSK scale.