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Papers by Kevin Clahan

Japanese Geotechnical Society special publication, 2024

Türkiye lies at the junction of three tectonic plates which drives the significant seismicity of ... more 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 over a distance of roughly 460 km, with both ruptures presenting typical left-lateral strike-slip geomorphology and surface rupture patterns. The investigation as part of the Geotechnical Extreme Events Reconnaissance teams included a regional assessment of the impacts to infrastructure (i.e., bridges, pipelines) as well as documentation of the geological effects (surface fault rupture, liquefaction, lateral spread, landslides). Here we present observations on rupture terminations and surface slip measurements along the M7.8 and M7.7 ruptures. Left-lateral surface displacements along the M7.8 EAF rupture were remarkably consistent, 3 to 4 m, but diminished to the south near Antakya to around 0.5 m. The M7.7 event produced the largest recorded surface displacements of consistent 7 to 8 m left-lateral offsets. Along both ruptures, the surface trace followed tectonic geomorphic features that would have been recognized in pre-rupture mapping such as linear swales, saddles, and side-hill benches. However, in other areas the ruptures are expressed by breaks across the tops of shutter ridges, through bedrock knobs, and complex arrays of en echelon pressure ridges.

AGU Fall Meeting Abstracts, Dec 1, 2019

field reconnaissance and requisite reporting for Kevin Clahan as part of LCI's internal grants pr... more field reconnaissance and requisite reporting for Kevin Clahan as part of LCI's internal grants program. The support of MRCE and LCI in this mission and report is gratefully acknowledged..

The Mw 6.3 Meinong earthquake, which struck southern Taiwan on February 6, 2016, was characterize... more The Mw 6.3 Meinong earthquake, which struck southern Taiwan on February 6, 2016, was characterized by an oblique left lateral strike-slip motion with a minor reverse component. The earthquake occurred at approximately 16 km depth on an unknown fault that did not rupture the ground surface, but rather produced a noticeable long period velocity pulse east to west, with the strongest amplitude motions recorded about 30km west of the epicentral region in Tainan City. Within this city, more than 20 multi-story buildings constructed under relatively modern building codes were severely damaged, including seven that suffered complete collapse. In addition, there was widespread damage associated with liquefaction, a substantial portion of which affected residential buildings causing large uniform and differential settlement, the later causing severe tilt to buildings in many cases. In response to this event, local earthquake professionals, faculty members, and students teamed with US NSF-spo...

Scientific Investigations Map, 2012

Geological Society of America Abstracts with Programs, 2018

Seismological Research Letters, 2015

This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthq... more This article summarizes the geotechnical effects of the 25 April 2015 M 7.8 Gorkha, Nepal, earthquake and aftershocks, as documented by a reconnaissance team that undertook a broad engineering and scientific assessment of the damage and collected perishable data for future analysis. Brief descriptions are provided of ground shaking, surface fault rupture, landsliding, soil failure, and infrastructure performance. The goal of this reconnaissance effort, led by Geotechnical Extreme Events Reconnaissance, is to learn from earthquakes and mitigate hazards in future earthquakes.

The California Geological Survey (CGS) has prepared a series of Seismic Hazard Zone Maps for a po... more The California Geological Survey (CGS) has prepared a series of Seismic Hazard Zone Maps for a portion of the southern San Francisco Bay of Northern California. Twelve 7.5-minute quadrangles (1:24,000 scale) have been released identifying areas that may be susceptible to earthquake-induced liquefaction or landsliding. Cities and Counties use these maps to identify areas requiring site-specific investigations prior to permitting

The Hersek Peninsula has been a strategic site for at least the last two millennia as a result of... more 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). Civilizations

2010 GSA Denver …, 2010

... ZELLMAN, Mark S. 1 , TURNER, James P. 1 , O'CONNELL, Daniel RH 2 , and CLAHAN, Kevin B. ... more ... ZELLMAN, Mark S. 1 , TURNER, James P. 1 , O'CONNELL, Daniel RH 2 , and CLAHAN, Kevin B. 3 , (1) Fugro William ... to geologic units from the “Preliminary Geologic Map of the Albuquerque – Rio Rancho Metropolitan Area and Vicinity, Bernalillo and Sandoval Counties, New ...

Journal of Geophysical Research, 1999

A late Holocene slip rate is proposed for the San Francisco Peninsula segment of the San Andreas ... more A late Holocene slip rate is proposed for the San Francisco Peninsula segment of the San Andreas fault zone at the Filoli Center, located between the town of Woodside and Upper Crystal Springs Reservoir, California. At this site the primary trace of the San Andreas fault zone traverses N35øW across the head of a large alluvial fan, offsetting buffed stream channel deposits. One deposit, with a minimum calibrated accelerator mass spectrometry (AMS) radiocarbon age of 2070 + 120 years B.P., is offset 30 + 2 m, yielding an average geologic slip rate of 17 + 4 mm yr-• for the late Holocene. A stratigraphically lower channel sequence, with a minimum calibrated AMS radiocarbon age of 330 + 200 years B.P., is offset 4.1 + 0.5 m. We interpret that this older sequence records both the penultimate earthquake on the peninsula segment, accompanied by 1.6 + 0.7 rn of dextral slip, and the ~2.5 rn of slip that occurred in 1906. On the basis of radiocarbon analyses and historical descriptions we propose that the pre-1906 earthquake occurred in June 1838. Our interpretations suggest that the San Francisco Peninsula segment of the San Andreas fault zone may rupture in earthquakes of at least two magnitudes: (1) a large-magnitude (•M w 8) event with a recurrence of• 250-320 years that involves the North Coast, San Francisco Peninsula, and Santa Cruz Mountains segments, as occurred in 1906 and (2) a M w 7.0-7.4, 1838-type event that ruptures only the San Francisco Peninsula segment. The apparent difference in slip rate of 7 + 7 mm-yr-• between the North Coast segment (24 + 3 mm yr-•) and the peninsula segment (17 + 4 mm yr-•) suggests a possible slip rate gradient on the northem Califomia section of the San Andreas fault.

Geosphere, 2011

Recent geologic mapping in the northern San Francisco Bay region (California, USA) supported by r... more Recent geologic mapping in the northern San Francisco Bay region (California, USA) supported by radiometric dating and tephro chronologic correlations, provides insights into the framework geology, stratigraphy, tectonic evolution, and geologic history of this part of the San Andreas transform plate boundary. There are 25 new and existing radiometric dates that define three tem porally distinct volcanic packages along the north margin of San Pablo Bay, i.e., the Bur dell Mountain Volcanics (11.1 Ma), the Tolay Volcanics (ca. 10-8 Ma), and the Sonoma Vol canics (ca. 8-2.5 Ma). The Burdell Mountain and the Tolay Volcanics are allochthonous, having been displaced from the Quien Sabe Volcanics and the Berkeley Hills Volcanics, respectively. Two samples from a core of the Tolay Volcanics taken from the Murphy #1 well in the Petaluma oilfield yielded ages of 8.99 ± 0.06 and 9.13 ± 0.06 Ma, demonstrat ing that volcanic rocks exposed along Tolay Creek near Sears Point previously thought to be a separate unit, the Donnell Ranch volcanics, are part of the Tolay Volcanics. Other new dates reported herein show that volcanic rocks in the Meacham Hill area and extending southwest to the Burdell Mountain fault are also part of the Tolay Volcanics. In the Sonoma volcanic field, strongly bimodal volcanic sequences are intercalated with sedi ments. In the Mayacmas Mountains a belt of eruptive centers youngs to the north. The youngest of these volcanic centers at Sugar loaf Ridge, which lithologically, chemically, and temporally matches the Napa Valley eruptive center, was apparently displaced 30 km to the northwest by movement along the Carneros and West Napa faults. The older parts of the Sonoma Volcanics have been displaced at least 28 km along the Rodgers Creek fault since ca. 7 Ma. The Petaluma Formation also youngs to the north along the Rodgers Creek-Hayward fault and the Ben nett Valley fault. The Petaluma basin formed as part of the Contra Costa basin in the Late Miocene and was displaced to its present location along the Rodgers Creek-Hayward and older faults. The Tolay fault, previously thought to be a major dextral fault, is part of a foldandthrust belt that does not exhibit lateral displacement.

Bulletin of the Seismological Society of America, 2006

Consideration of site conditions is a vital step in analyzing and predicting earthquake ground mo... more Consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion. The importance of amplification by soil conditions has long been recognized, but though many seismic-instrument sites have been characterized by their geologic conditions, there has been no consistent, simple classification applied to all sites. As classification of sites by shear-wave velocity has become more common, the need to go back and provide a simple uniform classification for all stations has become apparent. Within the Pacific Earthquake Engineering Research Center's Next Generation Attenuation equation project, developers of attenuation equations recognized the need to consider site conditions and asked that the California Geological Survey provide site conditions information for all stations that have recorded earthquake ground motion in California. To provide these estimates, we sorted the available shear-wave velocity data by geologic unit, generalized the geologic units, and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials. This new map is different from the California Geological Survey "preliminary site-conditions map of California" in that 19 geologically defined categories are used, rather than National Earthquake Hazards Reduction Program categories. Although this map does not yet cover all of California, when completed it may provide a basis for more precise consideration of site conditions in ground-motion calculations.