Tectonic setting of the Mendocino triple junction region
- Geological Survey, Menlo Park, CA (United States)
- Humboldt State Univ., Arcata, CA (United States)
Onshore and offshore geologic mapping coupled with topical investigations constrain the tectonic relations and geometry of active plate boundaries in the Mendocino triple junction region. Along the northern California coast and offshore, Gorda-North American plate convergence is reflected by youthful west- to northwest-verging thrust fault systems that extend to or near the plate interface at depth. Interplate coupling across a minimum breadth of 70--80 km is indicated by late Quaternary uplift and shortening rates, the nature and distribution of upper and lower plate seismicity, divergent trends in upper plate structures, and a history of large late Holocene earthquakes. Offshore seismic-reflection and seismicity data from the vicinity of the Mendocino fault (MF) show that the fault dips steeply to the north, and that the older, relatively rigid Pacific plate acts as a buttress against which the southern Gorda plate is being deformed. Onshore investigations show that the San Andreas fault zone (SAF) extends on land southeast of Point Delgada (at Whale Gulch), and is manifested along the north and northeast side of the King Range (KR) by north-northeast-vergent thrust faults. This thrust fault system may root into the steeply dipping offshore San Andreas fault. Faults of this system may include active, blind northeast-vergent thrusts that extend from a root zone beneath the King Range northward and upward into Franciscan Complex (Coastal belt) rocks along the north flank of the range. The southern Cascadia subduction zone megathrust intersects the Mendocino and San Andreas transform faults in the Mendocino triple junction. The upper crustal location of this intersection lies nearshore and/or landward along the north flank of the King Range. An area of focused rapid uplift and repeated coseismic growth (Mendocino Uplift) straddles the triple junction.
- OSTI ID:
- 5291068
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALIFORNIA
GEOLOGIC FAULTS
PLATE TECTONICS
GEOMETRY
MAPPING
SEISMIC SURVEYS
GEOLOGY
MARINE SURVEYS
OFFSHORE SITES
SEISMICITY
SUBDUCTION ZONES
DEVELOPED COUNTRIES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
MATHEMATICS
NORTH AMERICA
SURVEYS
TECTONICS
USA
580000* - Geosciences