| USGS | Central Region Geohazards Team |
REPORT FROM THE FIELD: 03 Sep 1999
17 August 1999 Izmet
(Kocaeli), Turkey, Earthquake:
Aftershock
Investigation Conducted by the U.S. Geological Survey (USGS) in Co-operation with Kandilli
Observatory & Earthquake Research Institute (KOERI), Boğaziçi University
The 17 August 1999 Izmet Earthquake killed thousands of people and left hundreds of thousands homeless as a result of damage to buildings. The primary purpose of the aftershock study is to investigate the correlation of the spatial pattern of earthquake damage with the geologic mechanisms that may have amplified the strong ground motions produced by the mainshock. We use portable seismographs to record aftershocks at sites in heavily damaged areas and also at a few sites in undamaged areas. We use the records from undamaged areas as references to estimate how much more strong shaking the damaged areas experienced. We also use the records from the damaged areas to study the details of how seismic waves propagate at those locations.
The USGS/KOERI team recorded ground motions throughout the region affected by the earthquake (Birgoren): both in the near-field or epicentral eastern zone -- Izmet, Golcuk, Adapazari, Korfez -- and at regional distances in the western zone 100 km away near Istanbal (first message from USGS Field Team, 23 Aug 1999).
We deployed 16 portable 3- and 6-component seismographs, 7 RefTek DASs equipped with L-22 seismometers and 9 Kinemetric K2s equipped with built-in force balance accelerometers (FBAs), at 18 stations. We recorded several hundred aftershocks; at least fifty by 4 or more stations. A magnitude 5.4 Mb (NEIS) aftershock occurred on 31 Aug at 08:10:50 UTC that was recorded (see also the Z, N, E components) by both strong-motion K2's in the East and weak-motion DAS's in the West. In general, one USGS/KOERI group focused on the epicentral region to the east of Istanbul, and the second group has focused on damage to the township of Avcilar, a suburb west of Istanbul.
East
Strong-motion K2's were deployed at the abutments of the proposed bridge across the Izmet Gulf (DOF, DOR), the oil refinery near Korfez (KOR, TUN, TUS, TUW), and the Toyota Plant (TYN, TYE) near Adapazari.
The magnitude 5.4 Mb aftershock was recorded by the small-aperture, strong-motion array at Korfez, and these records are shown in detail: P-wave, Z component; S-waves, N-S and E-W components, respectively. We calculated a Richter local magnitude of 5.2 ML from these local strong-motion records, which is the same magnitude assigned by the KOERI Seismology Observatory, and the P- and S-phase picks were emailed to NEIC.
West
The city of Istanbul experienced approximately one thousand deaths from the earthquake, and most of these were in the township of Avcilar. People whose apartments were destroyed or who feared the effects of further earthquakes lived in tents such as these in the highway cloverleaf next to the Avcilar Police Station.
We deployed the Avcilar Array that extended from about 5 km west (Station AT1, colocated with the KOERI strong-motion station ATS) of the damaged area of Avcilar to a fairly hard-rock site on Devonian outcrop (Station HL1) on the west side of Istanbul. The Avcilar and vicinity is underlain by soft Miocene rock composed of clays and carbonates that is as much as 200 m thick (excavation showing top 20 m near Station AR1). We also deployed a small-aperture tripartite array (Stations AB1, AC1, AD1 with ~200 spacing) in the damaged area of Avcilar and this array recorded a magnitude 5 aftershock on 29 Aug (Z, N, E).
Adapazari in the East
Adapazari was intensely and extensively damaged -- some parts completely destroyed -- by a combination of strong shaking and liquefaction (damage near Station YC0). We deployed a small-aperture, tripartite array (YA0, YB0, YC0) in the center of the damaged area two days before departure but no records have yet been recovered.
Acknowledgements
We dedicate this website to those who died, were injured, or suffered great loss in the Izmet Earthquake and to the hope that we will learn how to build communities that rest safely on the Earth. We are grateful to the people for the hospitality they extended to us in the midst of their tragedy, and we remember their cheerful strength.
Created 03 September 1999 in the
field at:
Earthquake Engineering Department
Kandilli Observatory &
Earthquake Research Institute
Istanbul, Turkey
