|
>>Research
EVALUATION OF INTEGRATED SEISMIC HAZARDS & GROUND FAILURE IN PULL-APART BASINS DURING THE IZMIT EARTHQUAKE IN TURKEY
GRADUATE RESEARCH ASSISTANT: Ismail Karatas (Graduated 2002)
COLLABORATORS: Dr. Stephen Wright (Co-PI), Mr. Jeff Bachhuber (William Lettis & Assoc.)
FUNDED BY : USGS National Earthquake Hazard Reduction Program (2001-2003)
DESCRIPTION
 
Figure 1. The Karamursel, Golcuk, and Lake Sapanca Pull-Apart Basins in Turkey (click thumbnails to see maps)
|
Ground failure and subsidence were prevalent throughout the region affected by the 1999 Kocaeli earthquake in Turkey, and thus, the Kocaeli earthquake provides an invaluable field laboratory from which to improve our understanding of earthquake effects. During this earthquake, some of the most remarkable and damaging examples of ground failure occurred within the Karamursel, Golcuk, and Lake Sapanca pull-apart basins in the near-fault region (Figure 1). Significant damage occurred in these pull-apart basins as a result of: (1) direct surface fault rupture; (2) tectonic subsidence and seawater intrusion; (3) lateral spreading and liquefaction; and, (4) tsunami drawdown and inundation. These phenomena were unusually concentrated within the stepover basins along the North Anatolian fault. The varied and concentrated earthquake effects in these pull-apart basins represent unique case histories of the interaction between different earthquake hazards and highlight the enhanced hazard within strike-slip fault stepovers.
The three goals of this study are:
- to determine the geometry of coastal failures within the pull-apart basins;
- to determine the failure mechanisms and interaction of earthquake effects;
- to correlate geologic and geotechnical conditions with the mechanisms of failure.
Towards these goals, year one of this study focused on collection of geologic and geotechnical data from the pull-apart basins. Year two of this study will concentrate on the geologic and geotechnical analyses aimed at evaluating the failure mechanisms of the coastal slides and correlating conditions with the failure mechanisms.
Based on earthquake reconnaissance reports and information from other researchers, ground failure/subsidence sites in or near the towns of Degirmendere, Seymen, and Esme were chosen for further investigation (Figure 1). All of these sites are located on Holocene delta fans and within pull-apart basins. The site investigation included rotary wash borings with standard penetration testing (SPT) every 1.5 m, and cone penetration test (CPT) soundings. The SPT borings and CPT soundings were performed by Zetas Earth Technology of Istanbul.
Degirmendere
In Degirmendere, a major coastal slide, extending approximately 300 m along the coast and 75 m inland, occurred at the nose of a delta fan. This delta fan had prograded into Izmit Bay and two restaurants and a hotel were located on the fan. Photographs of the pre- and post-earthquake shorelines are shown in Figure 2. A distinct scarp was observed along the post-earthquake shoreline, indicating a distinct slope failure. Cracking extended inland, beyond the extent of the coastal slide, but no evidence of liquefaction, such as soil ejecta, was observed. Three SPT borings and two CPT soundings were performed at Degirmendere (Figure 3).
 
Figure 2. Pre- and Post-Earthquake Shoreline at Degirmendere
|
Figure 3. Locations of SPT and CPT at Degirmendere |
Seymen
East of Golcuk, the MKE Scrapyard is located on a recent delta fan in the town of Seymen. A guardhouse and dock, for transportation of scrap, were located at the nose of the delta fan. During the earthquake, a slope failure occurred at the nose, and the guardhouse and dock slid into Izmit Bay (Figure 4). A series of ground cracks extending over 300 m inland were observed inland from the slide, but no soil ejecta was observed. Adjacent to the MKE Scrapyard is a tea garden that displayed significant lateral spreading and cracking, but no dramatic slope failure (Figure 5). Additionally, no soil vented through ground cracks. The tea garden is located on the same delta fan as the MKE Scrapyard, but is about 200 m west of the active nose of the delta. Further west of Seymen, a large area of coastal subsidence occurred along approximately a 2 km long coastline (Figure 6). Two SPT and five CPT were performed at the site in Seymen (Figure 7).
Figure 4. Slope failure at MKE Scrapyard in Seymen
|
Figure 5. Lateral Spreading at Tea Garden in Seymen
|
Figure 6. Coastal Subsidence West of Seymen
|
Figure 7. Locations of SPT and CPT at Seymen
|
Esme
The town of Esme is located along the north shore of Lake Sapanca and is situated on alluvium deposited from the hills north of the lake. A slide occurred along the coast in Esme, within delta sediments deposited by a creek (Figure 8). The area of the slide extended approximately 50 m along the coast and 35 m inland. The inland extension of ground cracks was about 150 m. Based on observations after the earthquake, ground cracks showed pure extensional movement with no rotational component and no evidence of liquefaction was observed. Post-earthquake photographs are shown in Figure 9. Two SPT and two CPT were performed at Esme (Figure 10).
Figure 8. Schematic of Ground Failure at Esme (EERI 2000)
|
|
Figure 10. Locations of SPT and CPT at Esme |
PUBLICATIONS
Rathje, E.M., Karatas, I., Wright, S.G., and Bachhuber, J. 2004. “Coastal Failures during the 1999 Kocaeli Earthquake in Turkey,” Soil Dynamics and Earthquake Engineering, 24(9-10), pp. 699-712.
Rathje, E.M., Wright, S.G., and Bachhuber, J. 2004. “Evaluation of Integrated Seismic Hazards and Ground Failure in Pull-Apart Basins during the 1999 Kocaeli Earthquake, Turkey,” Final Report to United States Geological Survey, Earthquake Hazard Reduction Program, February.
Rathje, E.M., Karatas, I., Bachhuber, J., and Wright, S.G. 2003. “Coastal Subsidence in Golcuk During the 1999 Kocaeli Earthquake in Turkey,” 13th International Offshore and Polar Engineering Conference, Honolulu, Hawaii, May, pp. 613-620.
Rathje, E.M., Wright, S.G., and Bachhuber, J. 2002. “Evaluation of Integrated Seismic Hazards and Ground Failure in Pull-Apart Basins during the 1999
Kocaeli Earthquake
,
Turkey
,” Report to
United States
Geological Survey, Earthquake Hazard Reduction Program, August.
Ismail Karatas (August 2002, co-advised with Stephen G. Wright) "Evaluation of Ground Failure in Pull-Apart Basins during the 1999 Kocaeli Earthquake," M.S. Thesis, Univ. of Texas at Austin
Bardet, J.P. and Seed, R.B, Cetin, K.O., Lettis, W., Rathje, E., Rau, G., and Ural, D. 2000. “Soil Liquefaction, Landslides, and Subsidence,” in Earthquake Spectra, The 1999 Kocaeli, Turkey, Earthquake Reconnaissance Report, Earthquake Engineering Research Institute, 16(A), pp. 141-162.
|
