Seismic reflection evidence for seismogenic low-angle faulting in southeastern Arizona

Journal Article · Wed Jul 01 04:00:00 EDT 1992 · Geology; (United States)

DOI:https://doi.org/10.1130/0091-7613(1992)020<0597:SREFSL>2.3.CO;2· OSTI ID:7202319

Johnson, R A; Loy, K L ^[1]

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1. Univ. of Arizona, Tucson (United States)

Focal mechanisms for large (M > 6) earthquakes in extensional terranes suggest that seismogenic normal faults have dips that range from {approximately}30{degree} to {approximately}70{degree}. Geologic relations suggest that low-angle faults have accommodated large-scale upper-crustal extension. These disparate observations are often reconciled by arguments that low-angle faults move aseismically or rotate to low angles from initially high angles. Seismic reflection data from the Tucson basin in southeast Arizona image a low-angle normal fault (the Santa Rita fault) that crops out along the trend of late Quaternary fault scarps caused by large-magnitude (M {approximately} 6.7-7.6) earthquakes. Velocity-independent dip analysis from shot records of the Santa Rita fault indicates that it has a true dip of {approximately}20{degree} to a depth of at least 6km. This observation suggests that low-angle extensional faults indeed may be seismogenic and that actual mechanisms for accommodation of upper-crustal extension depend on local conditions of stress and preexisting geologic structure.

• OSTI ID: 7202319
• Journal Information: Geology; (United States), Journal Name: Geology; (United States) Vol. 20:7; ISSN GLGYB; ISSN 0091-7613
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
ARIZONA
DEVELOPED COUNTRIES
EARTHQUAKES
FEDERAL REGION IX
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOMETRY
GEOPHYSICAL SURVEYS
MATHEMATICS
NORTH AMERICA
ORIENTATION
ORIGIN
SEISMIC EVENTS
SEISMIC SURVEYS
SEISMOLOGY
SURVEYS
USA