Late Quaternary history of paleoseismic activity along the Hohhot Segmentof the Daqingshan piedmont faultin Hetao depression zone, North China

Y. Ran, P. Zhang, L. Chen

Abstract


The Daqingshan Piedmont Fault (DPF) is one of the major active normal faults in the Hetao depression zone in the
northern part of Ordos Block, North China. It extends in NEE direction along the Daqingshan piedmont zone in the
eastern part of the depression, dipping to the south, for a length of 223 km. The fault formed in the Eocene and underwent
strong movement during the Cenozoic time. Its vertical displacement amplitude has exceeded 2400 m since the
Quaternary. The fault can be divided into 5 active segments. Paleoseismological studies were concentrated on its
western part from Baotou to Tumdzuoqi whereas the Hohhot Segment to the east was scarcely studied. To fill this gap
of knowlegde, the authors carried out in-depth study on the Daqingshan piedmont fault during recent years. Excavation
of trenches at Kuisu, Ulanblang, and Bakouzi sites on the Hohhot Segment of the Daqingshan piedmont fault
and study of geomorphic surfaces allow us to identify and date paleoearthquakes and to evaluate the completeness of
paleoseismic activity history. This was done both for the individual sites and for the entire segment since the Late
Quaternary using the «method for displacement confining» along the fault and «method for correlation between multiple
trenches». In this paper we present the geological loggings of two trenches at Kuisu site, provide the evidence
for 6 events since 19 ka BP and the cumulative displacement amount produced by them is around 7 m. But the cumulative
displacement amount obtained from difference in heights of geomorphic surfaces is 5.??.5.5 m. Results of tests
using the method of displacement confining show that the event sequence revealed at this site can be considered complete.
The data supplemented with information obtained in the Ulanblang and Bakouzi trenches show that 7 paleoseismic
events occurred on the Hohhot Fault Segment since 19 ka BP, i.e. they occurred at 18.75 ± 0.75 ka, 16.97 ±
± 0.96 ka, 14.65 ± 0.67 ka, 11.82 ± 0.69 ka, 9.45 ± 0.26 ka, 6.83 ± 0.26 ka, and 4.50 ± 0.23 ka BP, respectively, and
the average recurrence interval is 2.375 ± 0.432 ka. These results basically reflects the history of paleoseismic activity
on the fault segment in this period of time.

Keywords


Daqingshan piedmont fault (China);Hohhot Segment;paleoearthquakes;seismichistory;completeness of paleoseismic record

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References


DOI: https://doi.org/10.4401/ag-3445
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X