Recent geodynamics of major strike-slip zones

Abstract

Active strike-slip faults Historical seismicity Paleoseismicity Temporal variations of focal mechanisms of earthquakes Rates of accumulation of strike-slip deformation a b s t r a c t The subject of this study is strike-slip fault zones, where temporal variations of accumulation in strike-slip deformation complicate the standard process of deformation accumulation and release during strong earthquakes. These temporal variations are expressed in the El Ghab segment of the Dead Sea Transform zone (DST, Eastern Mediterranean) and in the Talas-Fergana fault zone (Central Asia). According to Global Positioning System (GPS)data, the strike-slip deformations within these zones are not now accumulating or are accumulating at a rate that is significantly less than their average rate during the Holocene and Quaternary or the PlioceneeQuaternary. Simultaneously, weak transverse shortening has been measured in both zones by GPS. In both of these zones, strong earthquakes have not registered within the XX century, yet epochs of intensified seismicity (strong earthquakes) took place throughout history. In the southern and central parts of the El Ghab zone, there is evidence of 30 strong historical earthquakes of Ms ! 5.7; however, no instrumental earthquakes of Ms ! 5 have been identified. The temporal distribution of seismic energy released by these earthquakes demonstrates a 350 ± 50-year cycle. Values for the seismic energies released during the peak phases of these cycles are approximated by a sinusoid that suggests the possibility of a !1800-year cycle ("hyper-cycle"), which began around the 3rd century, reached its maximum in the 12th century, and has continued until now. A combination of geological, archaeoseismological, and geodetic data show that the rate of sinistral strike-slip deformation varied in the fault zone, probably in conformity with the variation of seismicity during the "hyper-cycle." In the Talas-Fergana fault zone, trenching and 14 C dating that was correlated with right lateral offsets, gave a possible preliminary estimate of the average rates of the Late Holocene strike slip of about 10 mm per year, with a decrease in the SE direction to 4 mme4.5 mm per year. These studies also showed that the slip in the Talas-Fergana fault zone was realized mainly during strong earthquakes. New trenching and 14 C dating of paleoearthquake records identified the epoch of seismicity intensification dating to the XIVeXVII centuries. These paleoearthquakes could produce a total dextral slip at several meters. Therefore, consideration of these epochs was necessary to determine a calculated average slip rate during the Late Holocene.The main shock and the strongest aftershocks of the Altai earthquake of September 27, 2003, with Ms ¼ 7.0 demonstrated a strike-slip focal mechanism with an NW-trending

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

“…Paleoseismic data suggest that the TFF produced a series of strong earthquakes in the fourteenth to seventeenth centuries, with potential coseismic lateral offsets of several meters (Korjenkov et al, ; Trifonov et al, ). Despite the dense catalog of radiocarbon dates, these published studies do not present stratigraphic relationships between the dated Quaternary units and the fault zones.…”

“…We reinvestigated the Kyldau valley where cumulative ridges and streams are offset from 12 to 250 m (Burtman et al, 1996;Korzhenkov, Rogozhin, et al, 2014;Trifonov et al, 2015). The only prior geochronological constraint in the area is a radiocarbon age of 3,670 ± 80 14 C years B.P.…”

“…These include paleoseismic investigations along the TFF, focusing on morphological analysis of offset streams and ridges. The first field measurements of offsets along the fault and the first radiocarbon ages collected from associated organic sediments were made in the 1990s (Burtman et al, ; Trifonov et al, ). These authors assumed that the onset of organic deposition in sag ponds along the TFF could be related to seismic events.…”

Source-to-sink dynamics in the Kyrgyz Tien Shan from the Jurassic to the Paleogene: Insights from sedimentological and detrital zircon U-Pb analyses

“…Several studies (e.g. Burtman, 2012;Korzhenkov et al, 2014;Feld et al, 2015;Tibaldi et al, 2015) pointed out that the TFF is still active, with an average slip rate estimated at ~9-14 mm/a based on radiocarbon dating of terraces displaced by the fault (Burtman et al, 1996;Trifonov et al, 2015).…”

NATO and earth scientists: an ongoing collaboration to assess geohazards and contribute to societal security in Central Asia and the Caucasus

“…6). The ~700 km length of the fault is characterised by the typical features associated with paleoseismic deformation, including scarps, offset streams and drainage divides, as well as landslides (Burtman et al, 1987(Burtman et al, , 1996Trifonov et al, 1992Trifonov et al, , 2015Korjenkov et al, 2010Korjenkov et al, , 2012Korjenkov et al, , 2013Korzhenkov et al, 2014;Tibaldi et al, 2015;Rust et al, 2018). Nevertheless, modern seismic networks reveal only small and rare moderate seismicity along the fault zone, whereas GPS measurements do not provide any evidence of active deformation along the Talas-Fergana Fault, suggesting it is presently locked.…”