English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The October 17,1989 Loma Prieta earthquake produced coseismic ground deformation in the urbanized area along the northeastern flank of the Santa Cruz Mountains. This ground deformation was coincident with the general trend and locations of the Berrocal, Monte Vista, and Shannon faults, and is consistent with coseismic movement on these structures (Haugerud and Ellen, 1990). These faults are part of a series of southwest-dipping reverse faults that border the Santa Cruz Mountains range front and traverse the communities of Los Gatos, Saratoga, Cupertino, and Los Altos Hills. These faults, which deform the Pliocene and Pleistocene Santa Clara Formation and overlying Quaternary deposits, pose a potentially significant earthquake hazard to Santa Clara Valley. Possible movement along these faults during the 1989 Loma Prieta earthquake, and similar reported surface deformation during the 1906 earthquake (Lawson, 1908), suggests that the range-front faults may be Holocene active faults related at depth to the San Andreas fault This research provides a basic geologic and geomorphic framework to address whether these faults are independent seismic sources, or if displacement occurs only as secondary deformation during large-magnitude events on the San Andreas fault. The primary objective of this study is to determine the nature and pattern of late Quaternary tectonic deformation along the eastern Santa Cruz Mountains range front. Our mapping of late Quaternary deposits between Los Altos Hills and Los Gatos shows that several potentially fault-related geomorphic features are present along the range front coincident with the previously mapped Monte Vista and Shannon faults. In addition, there is substantial geomorphic evidence of surficial deformation in coalescent alluvial-fan deposits northeast of the range front coincident with the inferred Cascade fault (California Department of Water Resources [CDWR], 1975). The pattern of en echelon topographic and vegetation lineaments are evidence of distributed contractional deformation within a zone at least 5 km wide northeast of the range front Longitudinal profiles of late Quaternary fluvial terraces preserved along Saratoga, Stevens, and Los Gatos Creeks are used to identify the locations of deformation across the range front Terraces flanking Stevens Creek and topographic lineaments mapped during this study constrain the southwest dip of the main trace of the Monte Vista fault between about 40° and 50°. Minimum vertical separation across the range front of the highest late Pleistocene terrace within Stevens Creek canyon is 12 ± 1 m. Based on previous ageestimates of this terrace and a correlative fan surface, we estimate a late Pleistocene uplift rate of 0.3 ± 0.2 mm/yr for the Monte Vista fault. Based on a fault dip of about 45° southwest, a reverse dip-slip rate for the Monte Vista fault of 0.4 ± 0.3 mm/yr is estimated. Northwest-trending zones of anomalous stream gradients located about 4 to 6 km northeast of the range front are spatially coincident with potentially fault-related lineaments. Longitudinal profiles of streams crossing the lineament zones show local convexities consistent with tectonic uplift. Changes in stream sinuosity and fan distribution across the zones are also consistent with tectonic uplift. The deformed geomorphic surfaces and probable fault-related topographic lineaments mapped during this study provide strong evidence of late Quaternary faults located further east of the range front than previously recognized. The geomorphic features are consistent with deformation within the hanging walls of buried thrust faults east of previously mapped faults.

Geomorphic investigations of deformation along the northeastern margin of the Santa Cruz Mountains