New Zealand Journal of Geology and Geophysics abstracts
Paleoseismicity of the northern Horohoro Fault, Taupo Volcanic Zone, New
Zealand
JUDITH ZACHARIASEN*
RUSS VAN DISSEN
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
*Present address: Whitman College, Geology Department, Walla Walla, Washington
99362, U.S.A.
Abstract Trench excavations have provided constraints on the
recent paleoseismic history of the northern Horohoro Fault, one of the faults
of the Taupo Fault Belt (TFB), a belt of northeast-striking normal faults that
run along the axis of the Taupo Volcanic Zone (TVZ). We excavated two trenches
across the northernmost part of the fault where it displaces two Quaternary
terraces of different ages. The trench exposures reveal a series of alluvial
and volcanic fall deposits, ranging in age from c. 25 to 1.75 ka, that are
vertically displaced across the steeply southeast-dipping fault. The trench
data confirm that the fault is active and indicate that it has ruptured at
least three times within the last c. 26 000 yr and twice within the last
c. 15 700 yr, with an average vertical component of displacement of c. 1.1
m per rupture. The most recent surface rupture occurred between 1750 and 8050
yr ago. Because the fault has ruptured within the last 20 000 yr, we
consider it to be part of the modern TFB, the region that accommodates most of
the modern extension in the TVZ. The post-c. 25 ka vertical displacement rate
on the northern Horohoro Fault, which runs along the northwest boundary of the
TFB, is 0.14-0.2 mm/yr at the trench site, lower than that of many of the
faults within the modern TFB. It is unclear if the whole Horohoro Fault or just
the northern section is active. If the latter, then the fault may only be
accommodating strain associated with a bend or step in the TFB near Rotorua.
Keywords Taupo Volcanic Zone; paleoseismology; neotectonics;
earthquake; Horohoro Fault; trenching; Rotorua
New Zealand Journal of Geology & Geophysics, 2001, Vol 44: 391-401
0028-8306/01/4403-0391 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (3884K); (scanned from paper original: notes about this process)
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