Ozgur Kozaci

• PhD
• Principal Geologist at Pacific Gas and Electric Company

Paleoseismologic trenches excavated across the eastern part of the North Anatolian fault at Yaylabeli, Turkey, provide evidence for five surface ruptures during the past 2000 yr. We interpret these events as: (1) the historical 1939 M(w) 7.9 earthquake; (2) the historical 1254 A. D. earthquake; (3) the historical 1045 A. D. earthquake; (4) an earth...

Tree ring analysis provides a precise dating source for characterizing the timing of natural hazards. Specifically, seismogenic disturbances on trees have been successfully documented on major faults such as the San Andreas fault in California or Denali fault in Alaska. In this study, dendroseismology was employed along a 15-km-long stretch of the...

Seismic surveys were performed using a novel application of combined active and passive surface wave methods to evaluate the integrity of levees protecting islands in the Sacramento‐San Joaquin Delta, California, USA, from flooding. Delta islands have been undergoing rapid subsidence during the past century due to farming practices that have led to...

Understanding fault rupture deformation patterns, especially in complex fault zones, has fundamental implications on seismotectonic studies and hazard mitigation for the built environment. The 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake ruptures offer an opportunity to quantify deformation patterns and surface displacements from a complex fault ru...

The northern branch of the North Anatolian Fault (NAF) is the primary source of the greatest natural hazard for the Marmara Megapolis and specifically the İstanbul Metropolitan area. The Sea of Marmara section of the NAF is a ∼125-km-long seismic gap bound by the M7.4 1912 Mürefte earthquake rupture in the west and M7.4 1999 İzmit earthquake ruptur...

The 6 February 2023 Türkiye earthquakes and the accompanying aftershocks were a once-in-a-century catastrophe that has greatly impacted Türkiye and Syria. The repercussions of these events will have a lasting effect on the entire region. This article documents the geotechnical and geological observations performed by GEER (Geotechnical Extreme Even...

Türkiye lies at the junction of three tectonic plates which drives the significant seismicity of the region. The mainshock event of M7.8 occurred on a portion of the plate boundary East Anatolian Fault and was followed approximately 9 hours later by a M7.7 aftershock on the Sürgü - Çardak Fault. Surface fault rupture of these two events extends ove...

The Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence occurred on 4 and 5 July 2019 within the eastern California shear zone of southern California. Both events produced extensive surface faulting and ground deformation within Indian Wells Valley and Searles Valley. In the weeks following the earthquakes, more than six dozen scientists from governme...

Surface rupture in the 2019 Ridgecrest, California, earthquake sequence occurred along two orthogonal cross faults and includes dominantly left-lateral and northeast-striking rupture in the Mw 6.4 foreshock and dominantly right-lateral and northwest-striking rupture in the Mw 7.1 mainshock. We present >650 field-based, surface-displacement observat...

Surface traces of the Quaternary active Kern Canyon and Breckenridge faults were mapped via aerial reconnaissance, analysis of light detection and ranging (LiDAR) elevation data, review and interpretation of aerial photography, field reconnaissance, and detailed field mapping. This effort specifically targeted evidence of late Quaternary surface de...

Th e western termination of the 1999 İzmit earthquake still remains as an intriguing problem for researchers and the people residing around the Sea of Marmara. Th ere have been numerous off shore mapping and modelling studies performed in the Gulf of İzmit. However, the main debate about the western termination of the 1999 İzmit surface rupture is...

The Peninsula section of the San Andreas Fault is a significant hazard for the San Francisco Bay area, but little is known about the timing of earthquakes on this section of the fault prior to the great earthquake of April 18, 1906. An earthquake in 1838 resulted in strong shaking on the San Francisco Peninsula. Estimates of the magnitude of the 18...

The north-striking Breckenridge fault occurs along the 11-km-long western margin of Walker Basin, a west-tilted intermontane alluvial basin in the southern Sierra Nevada. This east-dipping normal fault has prominent geomorphic expression in the form of east-facing fault scarps on alluvial-fan deposits and distinct triangular facets of granitic bedr...

The Kern Canyon fault is a major N-S striking crustal structure that has accommodated extensional deformation within the southern Sierra Nevada range via dominantly east-down faulting since at least the middle Pleistocene. A 34-km-long portion of this fault, the Lake Isabella section, strikes N10°W between the towns of Kernville and Havilah and is...

The Hersek Peninsula has been a strategic site for at least the last two millennia as a result of its location. It extends into Izmit Bay and creates a shortcut for the historical Bagdad Road, an important section of the spice route, between Istanbul (Constantinople) and Iznik (Nicaea). It also controls the entrance of Izmit Bay to Izmit (Nicomedia...

Measurement of a stream offset and cosmogenic dating (10Be) of the alluvial surface into which the stream incised yield a preferred late Holocene slip rate of 18.6 +3.5/-3.3 mm a-1 for the central part of the North Anatolian fault (NAF) at Tahtaköprü, Turkey; use of variable cosmogenic production rate (VPR) models yields a slightly slower rate of ˜...

The behavior of major active faults at various temporal and spatial scales is one of the most fundamental, unresolved problems in modern tectonics. Determining the degree to which fault loading and strain release rates are constant (or non-constant) and documenting past earthquake occurrences are key approaches for understanding this phenomenon. We...

Understanding whether strain loading and release rates on major faults are constant or not in time is one of the major, unresolved questions in active tectonics. As part of our ongoing studies of the North Anatolian fault (NAF) in Turkey, we mapped the offset of a drainage that has incised into a mid-late Holocene alluvial fan along the NAF in nort...

Geomorphologic mapping and cosmogenic radionuclide (36Cl) dating of an offset fluvial terrace yield a preferred late Holocene slip rate of 20.5 {+/-} 5.5 mm/yr for the central part of the North Anatolian fault, Turkey; an independent slip rate constrained by 14C ages is 20.5 {+/-} 8.5 mm/yr. These rates are generally similar to, but possibly slight...

The degree to which fault loading and strain release rates are constant is one of the most fundamental, unresolved issues in modern tectonics. Are fault slip rates constant over all but the shortest time scales, as would be expected if faults are loaded steadily by plate tectonics? Or are slip rates variable at time scales of a few to a few dozen e...

Paleoseismologic trenches excavated across the North Anatolian fault near the village of Cukurcimen in north-central Turkey yield a complete record of surface ruptures for the past 2500 yr. The trenches provide mutually consistent evidence for the timing of the five most recent surface ruptures at the site, as well as at least two older events. The...

The Akşehir fault is one of the most important faults reflecting internal deformation of the Anatolian block. Small to medium magnitude earthquakes due to this fault are known from both historical and instrumental records. The last earthquake was aearly in 2002 (Mw=6.2) and it resulted in structural damage and loss of life. The surface deformations...

Understanding the temporal and spatial distribution of strain storage and release on major faults is a key aspect of modern geodynamics. Over the past 15 years GPS measurements have provided increasingly detailed velocity fields along numerous plate boundaries. In contrast, in many locations too few intermediate- and long-term geologic fault slip r...

"Are fault loading and strain release rates constant in time and space?" This is a fundamental but as-yet unanswered question in active tectonics. In order to assess the constancy of fault loading rates, it is necessary to determine slip rates at a variety of locations along the fault and at a variety of time scales. GPS (global positioning system)...

We analyze ground-penetrating radar (GPR) profiles made across and parallel to the August 1999 earthquake ruptures of the North Anatolian fault in Turkey. The profiles document cumulative right-lateral offset of stream channels and the successive faulting of a medieval (Ottoman) canal. The dominance of fine sand to coarse gravel in the sections ima...

The 1999 Ms 7.4 Izmit earthquake produced more than 110 km of surface rupture along the North Anatolian fault. We present here ground-penetrating radar (GPR) profiles surveyed across and parallel to the 1999 Izmit earthquake ruptures at two sites along the Izmit-Sapanca segment. Fine sandy and coarse gravels favor the penetration depth and processe...

Results of trenching across the eastern Düzce Fault document that surface rupture has occurred repeatedly on the fault prior to the 1999 Düzce earthquake, and that offset during previous earthquakes occurred at the same location and with similar amounts and type of slip as that of the 1999 earthquake. The most recent pre-1999 earthquake on the faul...

The central North Anatolian fault (NAF) is a model opportunity to study long-term behavior of continental transforms because of its relative mechanical simplicity and long historic record of earthquakes. We excavated three trenches across the NAF at Cukurcimen, near Refahiye in north-central Turkey on the eastern part of the 1939 M7.9 surface ruptu...

Recent bathimetric data of the north half of the Marmara Sea obtained by French-Turkish Marine Project revealed the details of the geometric segmentation of the northern strand of the North Anatolian fault. According to this geometry this strand consists of three large realesing stepovers (pull-apart structures) between the Gulf of Izmit and the Ga...