Multisegment rupture in the 11 July 1889 Chilik earthquake (M_w 8.0–8.3), Kazakh Tien Shan, interpreted from remote sensing, field survey, and paleoseismic trenching

Abstract

The 11 July 1889 Chilik earthquake (Mw 8.0–8.3) forms part of a remarkable sequence of large earthquakes in the late nineteenth and early twentieth centuries in the northern Tien Shan. Despite its importance, the source of the 1889 earthquake remains unknown, though the macroseismic epicenter is sited in the Chilik valley, ~100 km southeast of Almaty, Kazakhstan (~2 million population). Several short fault segments that have been inferred to have ruptured in 1889 are too short on their own to account for the estimated magnitude. In this paper we perform detailed surveying and trenching of the ~30 km long Saty fault, one of the previously inferred sources, and find that it was formed in a single earthquake within the last 700 years, involving surface slip of up to 10 m. The scarp‐forming event, likely to be the 1889 earthquake, was the only surface‐rupturing event for at least 5000 years and potentially for much longer. From satellite imagery we extend the mapped length of fresh scarps within the 1889 epicentral zone to a total of ~175 km, which we also suggest as candidate ruptures from the 1889 earthquake. The 175 km of rupture involves conjugate oblique left‐lateral and right‐lateral slip on three separate faults, with step overs of several kilometers between them. All three faults were essentially invisible in the Holocene geomorphology prior to the last slip. The recurrence interval between large earthquakes on any of these faults, and presumably on other faults of the Tien Shan, may be longer than the timescale over which the landscape is reset, providing a challenge for delineating sources of future hazard.

Rate of Slip From Multiple Quaternary Dating Methods and Paleoseismic Investigations Along the Talas‐Fergana Fault: Tectonic Implications for the Tien Shan Range

“…This offset value is surprisingly high, but in the range of coseismic slips reported for large earthquakes. The calculated potential magnitudes are thus comparable with historical and paleoearthquakes reported for the Tien Shan range and its surroundings (Abdrakhmatov et al, ; Arrowsmith et al, ; Campbell et al, ).…”

“…During this earthquake, 13 fault patches were activated, with 3–4 m of average slip, with peak slip <14 m, corresponding to moment magnitudes M w ranging from 7.8 to 7.9 (Arrowsmith et al, ). In 1889, the Chilik earthquake ruptured at least 175 km, involving three oblique strike‐slip fault patches separated by step‐overs of several kilometers (Abdrakhmatov et al, ). The coseismic slips are estimated to reach up to 10 m for a potential magnitude M w 8.0–8.3.…”

“…The range is seismically active, having generated large intraplate earthquakes ( M > 7.5) over the past centuries along large‐scale E‐W faults. Active faults have been mapped from satellite images (Abdrakhmatov et al, ; Molnar & Dayem, ; Molnar & Qidong, ; Molnar & Tapponnier, ; Tapponnier et al, ) and Global Positioning System (GPS) data indicate that, at the longitude of Kyrgyzstan, shortening across the Tien Shan range is ~20 mm/year (Abdrakhmatov et al, ; Zubovich et al, ).…”

“…These offset landforms however are not associated with large earthquakes during the past century. Recent paleoseismological studies conducted in the eastern Tien Shan Range suggest that these large‐scale faults have the potential to be reactivated during large earthquakes ( M w > 7.5) and have long recurrence times (e.g., several thousand years; Abdrakhmatov et al, ; Campbell et al, , ; Grützner et al, ; Landgraf et al, )…”

Active tectonics, earthquakes and palaeoseismicity in slowly deforming continents

“…Korjenkov et al 2010;Campbell et al 2013Campbell et al , 2015. Reactivation of several inherited faults may result in complex ruptures, incorporating segments with different mechanisms (Abdrakhmatov et al 2016). Interestingly, the known historical events seem to be located along the northern and southern borders of the Tien Shan (Kalmetieva et al 2009;Landgraf et al 2016), despite comparable Quaternary singlefault slip rates across the Tien Shan (Thompson et al 2002) and continuously northward-decreasing GPS-velocities (Zubovich et al 2010).…”