scholarly journals Evolution of the Gorda Escarpment, San Andreas Fault and Mendocino triple junction from multichannel seismic data collected across the northern Vizcaino block, offshore northern California

1998 ◽  
Vol 103 (B10) ◽  
pp. 23813-23825 ◽  
Author(s):  
Nicola J. Godfrey ◽  
Anne S. Meltzer ◽  
Simon L. Klemperer ◽  
Anne M. Tréhu ◽  
Beate Leitner ◽  
...  
Keyword(s):  
Seismic Data ◽  
Triple Junction ◽  
San Andreas Fault ◽  
Northern California ◽  
San Andreas ◽  
Mendocino Triple Junction ◽  
Multichannel Seismic Data

Late Cenozoic paleogeographic reconstruction of the San Francisco Bay area from analysis of stratigraphy, tectonics, and tephrochronology

2021 ◽  
Author(s):  
Andrei M. Sarna-Wojcicki
Keyword(s):  
San Francisco ◽  
Sierra Nevada ◽  
Triple Junction ◽  
San Andreas Fault ◽  
San Francisco Bay ◽  
Central Valley ◽  
San Andreas ◽  
The Pacific ◽  
Mendocino Triple Junction ◽  
Marine Embayment

ABSTRACT The Neogene stratigraphic and tectonic history of the Mount Diablo area is a consequence of the passage of the Mendocino triple junction by the San Francisco Bay area between 12 and 6 Ma, volcanism above a slab window trailing the Mendocino triple junction, and crustal transpression beginning ca. 8–6 Ma, when the Pacific plate and Sierra Nevada microplate began to converge obliquely. Between ca. 12 and 6 Ma, parts of the Sierra Nevada microplate were displaced by faults splaying from the main trace of the San Andreas fault and incorporated into the Pacific plate. The Mount Diablo anticlinorium was formed by crustal compression within a left-stepping, restraining bend of the eastern San Andreas fault system, with southwest-verging thrusting beneath, and with possible clockwise rotation between faults on its southeast and northwest sides. At ca. 10.5 Ma, a drainage divide formed between the northern Central Valley and the ocean. Regional uplift accelerated at ca. 6 Ma with onset of transpression between the Pacific and North America plates. Marine deposition ceased in the eastern Coast Range basins as a consequence of the regional uplift accompanying passage of the Mendocino triple junction, and trailing slab-window volcanism. From ca. 11 to ca. 5 Ma, andesitic volcanic intrusive rocks and lavas were erupted along the northwest crest of the central to northern Sierra Nevada and deposited on its western slope, providing abundant sediment to the northern Central Valley and the northeastern Coast Ranges. Sediment filled the Central Valley and overtopped the Stockton fault and arch, forming one large, south-draining system that flowed into a marine embayment at its southwestern end, the ancestral San Joaquin Sea. This marine embayment shrunk with time, and by ca. 2.3 Ma, it was eventually cut off from the ocean. Fluvial drainage continued southwest in the Central Valley until it was cut off in turn, probably by some combination of sea-level fluctuations and transpression along the San Andreas fault that uplifted, lengthened, and narrowed the outlet channel. As a consequence, a great lake, Lake Clyde, formed in the Central Valley at ca. 1.4 Ma, occupying all of the ancestral San Joaquin Valley and part of the ancestral Sacramento Valley. The lake rose and fell with global glacial and interglacial cycles. After a long, extreme glacial period, marine oxygen isotope stage (MIS) 16, it overtopped the Carquinez sill at 0.63 Ma and drained via San Francisco valley (now San Francisco Bay) and the Colma gap into the Merced marine embayment of the Pacific Ocean. Later, a new outlet for Central Valley drainage formed between ca. 130 and ca. 75 ka, when the Colma gap closed due to transpression and right-slip motion on the San Andreas fault, and Duxbury Point at the south end of the Point Reyes Peninsula moved sufficiently northwest along the San Andreas fault to unblock a bedrock notch, the feature we now call the Golden Gate.

Microearthquake seismicity and tectonics of Coastal Northern California

1970 ◽  
Vol 60 (5) ◽  
pp. 1669-1699 ◽  
Author(s):  
Leonardo Seeber ◽  
Muawia Barazangi ◽  
Ali Nowroozi
Keyword(s):  
High Frequency ◽  
Fault Plane ◽  
San Andreas Fault ◽  
High Gain ◽  
Strike Slip ◽  
Fault System ◽  
Northern California ◽  
Fault Plane Solutions ◽  
Sharp Bend ◽  
San Andreas

Abstract This paper demonstrates that high-gain, high-frequency portable seismographs operated for short intervals can provide unique data on the details of the current tectonic activity in a very small area. Five high-frequency, high-gain seismographs were operated at 25 sites along the coast of northern California during the summer of 1968. Eighty per cent of 160 microearthquakes located in the Cape Mendocino area occurred at depths between 15 and 35 km in a well-defined, horizontal seismic layer. These depths are significantly greater than those reported for other areas along the San Andreas fault system in California. Many of the earthquakes of the Cape Mendocino area occurred in sequences that have approximately the same magnitude versus length of faulting characteristics as other California earthquakes. Consistent first-motion directions are recorded from microearthquakes located within suitably chosen subdivisions of the active area. Composite fault plane solutions indicate that right-lateral movement prevails on strike-slip faults that radiate from Cape Mendocino northwest toward the Gorda basin. This is evidence that the Gorda basin is undergoing internal deformation. Inland, east of Cape Mendocino, a significant component of thrust faulting prevails for all the composite fault plane solutions. Thrusting is predominant in the fault plane solution of the June 26 1968 earthquake located along the Gorda escarpement. In general, the pattern of slip is consistent with a north-south crustal shortening. The Gorda escarpment, the Mattole River Valley, and the 1906 fault break northwest of Shelter Cove define a sharp bend that forms a possible connection between the Mendocino escarpment and the San Andreas fault. The distribution of hypocenters, relative travel times of P waves, and focal mechanisms strongly indicate that the above three features are surface expressions of an important structural boundary. The sharp bend in this boundary, which is concave toward the southwest, would tend to lock the dextral slip along the San Andreas fault and thus cause the regional north-south compression observed at Cape Mendocino. The above conclusions support the hypothesis that dextral strike-slip motion along the San Andreas fault is currently being taken up by slip along the Mendocino escarpment as well as by slip along northwest trending faults in the Gorda basin.

Geodetic applications of laser ranging

1977 ◽  
Vol 284 (1326) ◽  
pp. 529-536 ◽  
Keyword(s):  
High Altitude ◽  
San Andreas Fault ◽  
Plate Motion ◽  
Laser Ranging ◽  
Northern California ◽  
San Andreas ◽  
Lageos Satellite ◽  
Made In

The measurement of intersite distances with laser ranging to satellites has been demon­strated during the last few years for distances of several hundred to several thousand kilometres with precisions of a few tens of centimetres. These techniques are now being tested across the San Andreas fault in California where it is hoped plate motion will be observable after several years of measurements. The first measurements, between sites in southern and northern California, were made in 1972 and repeated again in 1974 with agreement between the baselines for each of the two years at the 10 cm level. The next measurements are planned for the summer of 1976. The results of these and related experiments will be described together with simulations of the projected capability using the high altitude Lageos satellite. General plans for future experiments will be described.

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