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

Abstract

On 17 August 1999 the M w 7.5 İzmit, 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 M w 7.1 Düzce, Turkey, earthquake produced a 40-km-long surface 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 easternmost segment of the August event, as well as on the western 20 km of the November 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 August surface rupture (i.e., a 5-km-wide zone of no surface rupture, as well as a 25Њ 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 Düzce 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.

Temporal Changes of Shallow Seismic Velocity Around the Karadere-Düzce Branch of the North Anatolian Fault and Strong Ground Motion

“…Among those, 28 clusters occurred around the Eften Lake, where the surface trace of the _ Izmit main shock terminated. Three months later, this segment reruptured during the Du¨zce main shock (e.g., HARTLEB et al, 2002). The 28 clusters in the Eften Lake area are in the depth range of 5-10 km, and appear to be on a fault plane dipping $65 o north (UTKUCU et al, 2003).…”

Evaluation of the seismicity for the Marmara region with statistical approaches

“…To the west near Golyaka, there is a sharp change (> 30 • ) in the strike of the northern branch of the NAFZ from EW to NE-SW. The NE-SW (Hartleb et al 2002). The southern branch was completely broken by the 1944 Bolu-Gerede, 1957 Abant, and 1967 Adapazari earthquakes.…”

Coseismic ruptures and tectonic landforms along the Düzce segment of the North Anatolian Fault Zone (Ms 7.1, November 1999)

“…In general, the 40‐km‐long coseismic rupture is simple and narrow with a deformation zone 0.5 to 5 m wide with local exceptions where the width reaches 50 m. The coseismic ruptures do not exactly run at the mountain‐piedmont interface, but affect both basin infill deposits and bedrock with a slightly northward convex trajectory. Owing to the strike variability of the rupture, transpressional and transtensional structures formed along the fault trace [ Akyüz et al , 2002; Hartleb et al , 2002] (Figure 2b). On the basis of geometry and the coseismic slip distribution, Akyüz et al [2002] divided the entire Düzce rupture into four sections (Figure 2b), each of them showing a symmetric slip tapering off toward both ends.…”