Publication Date:
2017-04-04
Description:
Seventy-five years after the destructive Chirpan earthquake of 14 April 1928, we
conducted a paleoseismologic study of the causative fault combining a review of
contemporary literature, geomorphology, geophysical prospecting, and trenching. We
reidentified the fault scarp in the field, and mapped it over a distance of 12.5 km.
Geophysical profiles and boreholes demonstrate that Chirpan scarp is the surface
expression of a normal fault that was active throughout the Pleistocene and Holocene. In
2002, we excavated a paleoseismologic trench to study the faulting history. A narrow fault
zone separates Plio-Pleistocene alluvial sand in the footwall from Holocene alluvial and
colluvial silt in the hanging wall. The 1928 earthquake is recorded by 0.45 m vertical
offset of the topsoil, in accordance with contemporary descriptions. We identified three
colluvial wedge-like units in the hanging wall sediments next to the fault, evidencing
at least three surface-rupturing paleoearthquakes since the Atlantic. Their timing could
only be loosely constrained using pollen. The penultimate event had an offset of 0.40–
0.45 m and occurred after circa 2600 calibrated years before present (cal years B.P.). Event
3 displaced a Subboreal semiarid calcic soil 0.55–0.70 m between circa 5750 and
2600 cal years B.P. The fourth event had a minimal offset of 0.50–0.70 m and occurred
between circa 8900 cal years B.P. and 4900 B.C., when the region was first settled.
We obtain a Holocene fault slip rate of 0.22 ± 0.12 mm/yr and an average recurrence
interval of 2350 ± 643 years for earthquakes comparable to or larger than the 1928 event.
Description:
Published
Description:
B01303
Description:
JCR Journal
Description:
reserved
Keywords:
Chirpan earthquake
;
1928
;
PaleoseismologY
;
Bulgaria
;
04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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