Air-temperature control on diurnal variations in microseismicity at Laohugou Glacier No. 12, Qilian Mountains

Abstract

We conducted a 9-d seismic experiment in October 2015 at Laohugou Glacier No. 12. We identified microseismic signals using the short-term/long-term average trigger algorithm at four stations and classified them as long and short-duration events based on waveform, frequency, duration and magnitude characteristics. Both categories show systematical diurnal trends. The long-duration events are low-frequency tremor-like events that mainly occurred during the daytime with only several events per day. These events lasted tens of seconds to tens of minutes and are likely related to resonance of daytime meltwater. The dominant short-duration events mostly occurred during the night time with a peak occurrence frequency of ~360 h−1. Their short-duration (<0.2 s), high frequency (20–100 Hz) and dominance of Rayleigh waves are typical of events for near-surface crack opening. A strong negative correlation between the hourly event number and temperature change rate suggests that the occurrence of night-time events is controlled by the rate of night-time cooling. We estimated the near-surface tensile stress due to thermal contraction at night to be tens of kilopascals, which is enough to induce opening of surface cracks with pre-existing local stress concentrations, although we cannot exclude the effect of refreezing of meltwater produced during the day.

Tidal and Thermal Stresses Drive Seismicity Along a Major Ross Ice Shelf Rift

“…Second, the uppermost portion of the ice experiences thermal contraction in response to rapid temperature drops and would thus be under tensional stress, as is observed for sea ice during cold weather (Dempsey et al, ; Evans & Untersteiner, ; Richter‐Menge & Elder, ). Similar behavior has been observed in some alpine glaciers, which exhibit thermal fracturing in response to cold nighttime temperatures (Podolskiy et al, ; Zhang et al, ). Although we have not obtained source parameters for these events, the association between the icequakes and tensional tidal stress, and their location in a rift zone, suggests that the events are dominantly tensional.…”

The influence of environmental microseismicity on detection and interpretation of small-magnitude events in a polar glacier setting

“…7), we consistently detect cracks of linear source scale ⩾1 m. Under summer conditions, we are able to reliably detect cracks of linear source scale ⩾1/3 m. These length scales are comparable to depth scales of thermal bending moments associated with freezing superimposed ice over a subsurface slush layer (0-150 cm, MacAyeal and others, 2018, Fig. 11), and diurnally variable thermal stresses (depthsˆ40-60 cm, Zhang and others, 2019).…”

Viscoelastic Modeling of Nocturnal Thermal Fracturing in a Himalayan Debris‐Covered Glacier

“…This in situ experiment presents an interesting test case for validating the existing theory on ice fracture and crevasse formation with the ability to compare the data against two different approaches to ice constitutive behaviour: that is, with or without elasticity (e.g., Attree et al, ; Sanderson, ; Zhang et al, ).…”

“…Similarly, the thermal bending of a frozen lid overlying slushy ice/water was associated with seismicity on an ice shelf in Antarctica (MacAyeal et al, ). To our knowledge, with the exception of a study in Tibet by Zhang et al (), the thermal contraction cracking of glacier ice has not been observed at temperate alpine glaciers (Neave & Savage, ) or in the ablation zone of the Greenland Ice Sheet, where dynamic stresses and hydrofracturing are dominant (Röösli et al, ).…”

“…These observations suggest that the thickness of the debris mantle has a major influence on the observed glacier seismicity, which the present study aims to elucidate, with a particular emphasis on exploring the constitutive behavior of ice in order to explain the observed behavior, and the thickness of debris mantle that is sufficient to protect the ice from contraction fracturing in a given environmental setting. This in situ experiment presents an interesting test case for validating the existing theory on ice fracture and crevasse formation with the ability to compare the data against two different approaches to ice constitutive behaviour: that is, with or without elasticity (e.g., Attree et al, 2017;Sanderson, 1978;Zhang et al, 2019).…”