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Lateral Offsets on Surveyed Cultural Features Resulting from the 1999 İzmit and Düzce Earthquakes, Turkey

Rockwell, Thomas K. and Lindvall, Scott and Dawson, Tim and Langridge, Rob and Lettis, William and Klinger, Yann (2002) Lateral Offsets on Surveyed Cultural Features Resulting from the 1999 İzmit and Düzce Earthquakes, Turkey. Bulletin of the Seismological Society of America, 92 (1). pp. 79-94. ISSN 0037-1106. doi:10.1785/0120000809.

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Surveys of offset linear cultural features that cross the surface ruptures of the 17 August and 12 November 1999 earthquakes on the North Anatolian fault in Turkey yield slip values as large as or larger than those recorded by near-field measurements in the same areas immediately after the earthquake. Using long, linear alignments of trees, fence lines, walls, and canals, we demonstrate as much as a 2-m increase in observed slip over the initial field measurements. On an average, we observed about 15% of the total lateral slip as off-fault deformation, with values ranging from 0% to 40% of the total slip. Part of this lateral deformation is accommodated by bending or drag in a zone as much as 30 m in width, although usually the zone varies between 5 and 20 m in width. This supports the idea that substantial nonbrittle, off-fault deformation is associated with ruptures in areas of alluvial fill. Alternatively, there may have been substantial afterslip, although none has been recognized on postearthquake repaired structures. Our observations suggest that postearthquake measurements of fault slip, using tape measures on offset geomorphic features, may underestimate the actual amount of slip in that event, where the nonlinearity of the offset feature does not allow recognition of the warping. Surveys of multiple tree lines within groves of poplar trees, planted in straight lines across the fault prior to the earthquake, show surprisingly large lateral variations. In one grove, slip increases by nearly 1.8 m, or 35% of the maximum measured value, over a lateral distance of nearly 100 m. This and other observations along the 1999 ruptures suggest that the lateral variability of slip observed from displaced geomorphic features in many earthquakes of the past may represent a combination of (1) actual differences in slip at the surface and (2) the difficulty in recognizing distributed nonbrittle deformation.

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Additional Information:© 2002 Seismological Society of America. Manuscript received 20 August 2001. We first and foremost thank the wonderful people of Turkey for welcoming us with open arms after such a terrible disaster. Many landowners granted access for the surveying work, and many local Turks provided useful discussions on individual features and their original configurations. We thank Pacific Gas & Electric Company for funding most of this project, and especially Bill Page for his direction during the early phases of the field investigation, but we accept full responsibility for any misinterpretations that may evolve out of this work. The Southern California Earthquake Center provided support for R. L. to fly over and join the surveying team. Finally, we thank Aykut Barka for his unwavering support and assistance in Turkey in all phases of our work, including providing students to help with translations. Without Aykut and his Turkish colleagues, work in Turkey would have been much more difficult and not nearly as much fun. This research was supported by the Southern California Earthquake Center. SCEC is funded by NSF Cooperative agreement EAR-8920136 and USGS Cooperative agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. The SCEC Contribution Number for this article is 615.
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Southern California Earthquake Center (SCEC)UNSPECIFIED
NSF Cooperative AgreementEAR-8920136
USGS Cooperative Agreement14-08-0001-A0899
USGS Cooperative Agreement1434-HQ-97AG01718
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Southern California Earthquake Center615
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Record Number:CaltechAUTHORS:20140801-081230123
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47762
Deposited By: Tony Diaz
Deposited On:01 Aug 2014 16:11
Last Modified:10 Nov 2021 17:50

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