The understanding of sea ice mass balance processes requires continuous monitoring of the seasonal evolution of the ice thickness. While autonomous ice mass balance (IMB) buoys deployed over the past two decades have contributed to scientists' understanding of ice growth and decay processes, deployment has been limited, in part, by the cost of such systems. Routine, basinwide monitoring of the ice cover is realistically achievable through a network of reliable and affordable autonomous instrumentation. This paper describes the development of a novel autonomous platform and sensor that replaces the traditional thermistor strings for monitoring temperature profiles in the ice and snow using a chain of inexpensive digital temperature chip sensors linked by a single-wire data bus. By incorporating a heating element into each sensor, the instrument is capable of resolving material interfaces (e.g., air-snow and ice-ocean boundaries) even under isothermal conditions. The instrument is small, low cost, and easy to deploy. Field and laboratory tests of the sensor chain demonstrate that the technology can reliably resolve material boundaries to within a few centimeters. The discrimination between different media based on sensor thermal response is weak in some deployments and efforts to optimize the performance continue.
The Lepsy fault of the northern Tien Shan, SE Kazakhstan, extends E‐W 120 km from the high mountains of the Dzhungarian Ala‐tau, a subrange of the northern Tien Shan, into the low‐lying Kazakh platform. It is an example of an active structure that connects a more rapidly deforming mountain region with an apparently stable continental region and follows a known Palaeozoic structure. Field‐based and satellite observations reveal an ∼10 m vertical offset exceptionally preserved along the entire length of the fault. Geomorphic analysis and age control from radiocarbon and optically stimulated luminescence dating methods indicate that the scarp formed in the Holocene and was generated by at least two substantial earthquakes. The most recent event, dated to sometime after ∼400 years B.P., is likely to have ruptured the entire ∼120 km fault length in a Mw 7.5–8.2 earthquake. The Lepsy fault kinematics were characterized using digital elevation models and high‐resolution satellite imagery, which indicate that the predominant sense of motion is reverse right lateral with a fault strike, dip, and slip vector azimuth of ∼110°, 50°S, and 317–343°, respectively, which is consistent with predominant N‐S shortening related to the India‐Eurasia collision. In light of these observations, and because the activity of the Lepsy fault would have been hard to ascertain if it had not ruptured in the recent past, we note that the absence of known active faults within low‐relief and low strain rate continental interiors does not always imply an absence of seismic hazard.
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.
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