Special Earthquake Report No: 99-017

Regional Location:

Preliminary Magnitude:

Moment Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Focal Depth (km):
Analysis Quality (A-D):


7.8 Ms (NEIC), 7.4 MD (KOERI)

Mw 7.4 (NEIC), Mw 7.5 (HRV)

15 km

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A powerful earthquake registering a preliminary magnitude of Ms 7.8 (NEIC), Mw 7.4 (NEIC fault plane solution), Mw 7.5 (Harvard fault plane solution), MD M7.4 (Kandilli Observatory and Earthquake Research Institute, Istanbul, Turkey) was detected 00:01:38 UTC, (3:02 a.m. local time), August 17, in western Turkey (See Map). The quake was centered about 32 miles southeast of Istanbul, Turkey, in the Gulf of Izmit located along the western Sea of Marama, near cities of Gebza, Izmit and Yalova.
The focal depth was placed at a depth of 15 km and the fault plane solution indicated pure right-lateral strike-slip motion along a east-west trending fault plane. Thousands of aftershocks have been recorded, including nearly a half dozen in the M5 range. Most of the aftershock activity is confined to the region between Izmit and Adapazari to the east of the epicenter. Here is a quick list of some of the larger events:
99/08/17 00:01:38 40.64N 29.83E 10.0 7.8Ms A TURKEY Main Shock
99/08/17 02:42:56 40.63N 30.85E 10.0 5.0Mb B TURKEY
99/08/17 03:14:00 40.66N 30.75E 10.0 5.3Mb A TURKEY
99/08/17 05:10:07 40.52N 30.43E 10.0 5.0Mb B TURKEY
99/08/17 09:02:10 40.75N 31.03E 10.0 4.9Mb B TURKEY
99/08/17 11:58:09 40.65N 30.15E 10.0 4.7Mb B TURKEY
99/08/17 22:12:48 40.68N 30.59E 10.0 4.1Mb A TURKEY
99/08/19 13:04:12 40.67N 30.82E 10.0 4.8Mb A TURKEY
99/08/19 15:17:45 40.58N 29.08E 10.0 5.0Mb A TURKEY
Click here for a current list of aftershocks from KOERI.
Field observations conduction by the Kandilli Observatory and Earthquake Research Institute (KOERI) in Istanbul, Turkey, have discovered surface fault ruptures between Lake Sapanca and the Sea of Marmara. The total length of the ruptures is estimated to be more than 150 km, some of which is submerged under the Gulf of Izmit and probably extending into the Sea of Marmara, with maximum displacements of about 4.9 m. For ongoing news of the geologic investigations, see the USGS or KOERI.
Preliminary reports indicate catastrophic damage has occurred with widespread causalities. Numerous buildings have collapsed in Istanbul, Izmit and other surrounding communities killing thousands of people and injuring tens of thousands. Rescue workers from the Turkish government and surrounding nations, including the United States, have been dispatched to the area. Turkish television have shown aerial pictures where numerous structures have collapsed into pancakes of rubble and steel, trapping numerous people. Numerous news reports are covering the rescue effort and links can be found below.
The damage from the initial tremor was particularly intense because of the shallow depth of the earthquake's focus, just 15 km below the surface. This means the shock waves are felt much more strongly at the surface than for deeper earthquakes.
Portions of the Armutlu Peninsula are under water because of localized subsidence failures. Aerial television footage shows numerous rock falls and some landslides. Numerous transportation routes are damaged and are blocking relief and scientific.
The quake occurred along the North Anatolian Fault, a prominent geologic structure which extends for over 800 miles through northern Turkey (Map 2). The Izmit Gulf and western Turkey has been hit several times in the last two millennia by large and damaging earthquakes (See list). Most recently, a M7.1 earthquake struck in July 1967 just 30 miles west of Izmit. Since 1939 there have been 11 quakes registering M6.7+ along the North Anatolian Fault.

Some technical reading of the North Anatolian Fault:
Progressive failure on the North Anatolian fault since 1939 by
earthquake stress triggering
; by Ross S. Stein 1, Aykut A. Barka 2 and James H. Dieterich
Space-time migration of earthquakes along the North Anatolian fault zone and seismic gaps; by M. Nafi Toksoz, A.F. Shakal, and Andrew J. Michael, Pageoph, Vol. 117, 1258-1270, 1979.
Report on the field trip along the North Anatolian Fault Zone (August 1-15, 1997) organized by Aykut Barka
Paleoseismology of the North Anatolian fault, Turkey; K. OKUMURA, T. YOSHIOKA and Ismail Kuscu [1993]
An active, deep marine strike-slip basin along the North Anatolian Fault in Turkey; A.I. Okay, E. Demirbag, H. Kurt, N. Okay, I. Kuscu
Slip Rate of The North Anatolian Fault, Turkey; A.Hubert , R.Armijo, B.Meyer, G.King, F.Gasse, A.Barka

News Articles:
Reuters, Thursday August 19
More photos
Red Cross

Update: 8:30 a.m., August 27, 1999.

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Subtract 8 hours from Greenwich Mean Time to obtain PST or 5 hours for EDT
Location Quality: A (good), B (fair), C (poor), D (bad)
Magnitude: Ml (local or Richter magnitude), Lg (mblg), Md (duration), Mb (body wave), Ms (surface wave), Mw (moment)

Standard Sources Include:
U.S. Geological Survey, National Earthquake Information Center, Golden, CO (NEIC)
Harvard Geophysical Observatory, Harvard University, Cambridge, MA (HRV)
U.S. Geological Survey, Northern California Seismic Network (NCSN)
University of California, Berkeley, Seismological Laboratory (UCBSL)
Southern California Seismic Network (USGS & Caltech), Pasadena, California (SCSN)
California Institute of Technology, Pasadena, California (Caltech)
various wire reports and/or personal communications

All data are preliminary and subject to change.
Copyright © 1999 Advanced Geologic Exploration, Inc.
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