2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 5
Presentation Time: 8:00 AM-12:00 PM


SYNOLAKIS, Costas E., Civil Engineering, University of Southern California, Los Angeles, CA 90089 and OKAL, Emile A., Department of Geological Sciences, Northwestern University, Evanston, IL 60208, emile@earth.northwestern.edu

For tsunamis occurring 40 to 60 years ago, we have found it possible to obtain detailed information on runup and inundation from elderly witnesses and to transform their recollections into a quantitative database, which can be later used in hydrodynamic simulations for the purpose of unraveling the mechanism of generation of the tsunami. After identifying witnesses in the affected communities, we work with native speakers to collect their testimonies on video tape, with a process of cross-examination designed to ensure their reliability. In most instances, we ask the witness to accompany us to the exact area of penetration, and proceed to make measurements of runup and inundation using standard leveling techniques. This procedure can work both in the near and far fields, and we describe our results in the Pacific for the 1946 Aleutian tsunami earthquake, and in the Aegean Sea for the 1956 Amorgos tsunami. In the case of the 1946 event, we have accumulated a dataset of more than 60 measurements from witnesses aged 59 to 89 at the time of the interview. The principal results are the re-evaluation of the runup at Scotch Cap at a record 42 m, and the revision of the runup at Juan Fernandez to only 2.7 m, a crucial observation as it requires strong lobes of directivity characteristic of dislocation sources in the far field. In the case of the 1956 Amorgos tsunami, the growing dataset presently contains 37 data points on six islands and the coast of Turkey, pointing out to significant lateral variations in runup and timing, suggestive of the implication of local underwater landslides.