South Island, New Zealand, and transverse ranges, California: A seismotectonic comparison

Abstract

Both the South Island of New Zealand and the Transverse Ranges of California have (1) a major right‐slip fault marking the plate boundary, (2) a left‐stepping bend in the fault resulting in ranges and basins bounded by active reverse faults that strike 45° counterclockwise to the regional strike of the main fault, (3) a set of right‐slip faults on one side of the constraining bend, with most of the total displacement concentrated On the fault stepped farthest left from the continuation of the fault on the other side of the bend, and (4) intersections between the set of faults and the main fault within the bend not present or poorly defined. The faults with most of the displacement (Alpine‐Wairau, San Andreas) may pre‐date the constraining bend, The reverse fault province southeast of the Alpine fault is separated from that fault by the Southern Alps, which may be underlain by crust that is too hot and too weak to sustain major reverse faults. Average reverse fault recurrence intervals in New Zealand and California are 10³ to 2 × 104 years as compared to less than 10³ years for the right‐slip master fault, Seismicity is high but patchy in the Nelson‐Buller region of the northern South Island, low but patchy in the Transverse Ranges, and very low in Central Otago in the southern South Island, all reverse fault provinces. Seismicity patterns in both regions, poorly related to overall late Quaternary fault distribution, correspond largely to individual rupture events on portions of Quaternary faults, and the seismic inactivity of many of these faults may simply represent quiescence between seismic faulting with long recurrence intervals. The geology and Seismicity of the three reverse‐fault provinces support the suggestion of C. R. Allen [1975] that late Quaternary fault history is a better long‐term guide for assessment of large‐magnitude earthquake hazard than instrumental and historical Seismicity for faults with long recurrence intervals.