Migratory earthquake precursors are dominant on an ice stream fault

Simple fault models predict earthquake nucleation near the eventual hypocenter (self-nucleation). However, some earthquakes have migratory foreshocks and possibly slow slip that travel large distances toward the eventual mainshock hypocenter (migratory nucleation). Scarce observations of migratory nucleation may result from real differences between faults or merely observational limitations. We use Global Positioning System and passive seismic records of the easily observed daily ice stream earthquake cycle of the Whillans Ice Plain, West Antarctica, to quantify the prevalence of migratory versus self-nucleation in a large-scale, natural stick-slip system. We find abundant and predominantly migratory precursory slip, whereas self-nucleation is nearly absent. This demonstration that migratory nucleation exists on a natural fault implies that more-observable migratory precursors may also occur before some earthquakes.

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Basal mechanics of ice streams: Insights from the stick-slip motion of Whillans Ice Stream, West Antarctica

Journal of Geophysical Research Atmospheres ◽

10.1029/2008jf001035 ◽

2009 ◽

Vol 114 (F1) ◽

Cited By ~ 63

Author(s):

J. Paul Winberry ◽

Sridhar Anandakrishnan ◽

Richard B. Alley ◽

Robert A. Bindschadler ◽

Matt A. King

Keyword(s):

West Antarctica ◽

Ice Streams ◽

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Stick Slip Motion ◽

Slip Motion

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The onset area of Ice Stream D, West Antarctica

Journal of Glaciology ◽

10.3189/172756500781833377 ◽

2000 ◽

Vol 46 (152) ◽

pp. 95-101 ◽

Cited By ~ 13

Author(s):

Robert Bindschadler ◽

Xin Chen ◽

Patricia Vornberger

Keyword(s):

Strain Rate ◽

Global Positioning System ◽

Landsat Imagery ◽

Surface Flow ◽

West Antarctica ◽

The Past ◽

Ice Stream ◽

Global Positioning ◽

Longitudinal Strain Rate ◽

Streaming Flow

AbstractSurface flow in a 10 000 km2 expanse of the onset area of Ice Stream D, West Antarctica, was measured by repeat, precise global positioning system surveys over a 1 year interval. The pattern of velocity and strain rate shows the development of Ice Stream D, the major flow into which originates south of Byrd station and follows the course of a deep bed channel. Plotting of the driving stress vs the ratio of velocity and ice thickness identifies the onset of streaming flow (roughly 140 km downstream of Byrd station) as a transition between deformation flow and sliding flow. Along the kinematic center line of the developing ice stream, the ice rheology is linear at stresses below 0.6 bar, and appears temperate at the base well before the onset of streaming is reached. The onset corresponds to a maximum driving stress of 0.8 bar. It occurs downstream of a slight increase in longitudinal strain rate where stronger along-flow lineations are apparent in Landsat imagery, and after the ice has passed the center of an overdeepening in the bed channel. No current deviation from equilibrium is detected in this region, but a set of flow stripes misaligned with present flow indicates significant changes in flow have occurred in the past.

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Tremor during ice-stream stick slip

The Cryosphere ◽

10.5194/tc-10-385-2016 ◽

2016 ◽

Vol 10 (1) ◽

pp. 385-399 ◽

Cited By ~ 21

Author(s):

B. P. Lipovsky ◽

E. M. Dunham

Keyword(s):

Large Scale ◽

Wait Time ◽

Stick Slip ◽

Repeating Earthquakes ◽

Ice Surface ◽

Ice Stream ◽

State Dependent ◽

State Evolution ◽

Spectral Peaks ◽

Balance Of Forces

Abstract. During the 200 km-scale stick slip of the Whillans Ice Plain (WIP), West Antarctica, seismic tremor episodes occur at the ice–bed interface. We interpret these tremor episodes as swarms of small repeating earthquakes. The earthquakes are evenly spaced in time, and this even spacing gives rise to spectral peaks at integer multiples of the recurrence frequency ∼ 10–20 Hz. We conduct numerical simulations of the tremor episodes that include the balance of forces acting on the fault, the evolution of rate- and state-dependent fault friction, and wave propagation from the fault patch to a seismometer located on the ice. The ice slides as an elastic block loaded by the push of the upstream ice, and so the simulated basal fault patch experiences a loading velocity equal to the velocity observed by GPS receivers on the surface of the WIP. By matching synthetic seismograms to observed seismograms, we infer fault patch area ∼ 10 m2, bed shear modulus ∼ 20 MPa, effective pressure ∼ 10 kPa, and frictional state evolution distance ∼ 1 μm. Large-scale slip events often occur twice daily, although skipped events have been increasing in frequency over the last decade. The amplitude of tremor (recorded by seismometers on the ice surface) is greater during the double wait time events that follow skipped events. The physical mechanism responsible for these elevated amplitudes may provide a window into near-future subglacial conditions and the processes that occur during ice-stream stagnation.

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Testing a model of earthquake nucleation

Bulletin of the Seismological Society of America ◽

10.1785/bssa0850061873 ◽

1995 ◽

Vol 85 (6) ◽

pp. 1873-1878

Author(s):

Rachel E. Abercrombie ◽

Duncan C. Agnew ◽

Frank K. Wyatt

Keyword(s):

Slow Slip ◽

Dynamic Rupture ◽

Short Term ◽

Landers Earthquake ◽

Earthquake Nucleation ◽

Short Term Prediction ◽

Stress Drops ◽

1992 Landers Earthquake ◽

Precursory Slip ◽

Laboratory Models

Abstract Some laboratory models of slip find that a critical amount (or velocity) of slow slip is required over a nucleation patch before dynamic failure begins. Typically, such patch sizes, when extrapolated to earthquakes, have been thought to be very small and the precursory slip undetectable. Ohnaka (1992, 1993) has proposed a model in which foreshocks delineate a growing zone of quasi-static slip that nucleates the dynamic rupture and suggests that it could be large enough (∼10 km across) to be detectable and thus useful for short-term earthquake prediction. The 1992 Landers earthquake (M 7.3) had a distinctive foreshock sequence and initiated only 70 km from the strain meters at the Piñon Flat Observatory (PFO). We use this earthquake to investigate the validity and usefulness of Ohnaka's model. The accurate relocations of Dodge et al. (1995) show that the foreshock zone can be interpreted as expanding from an area of 800 m (along strike) by 900 m (in depth), to 2000 by 3200 m in the 6.5 hr before the mainshock. We have calculated the deformation signals expected both at PFO and 20 km from the foreshock zone, assuming either constant slip or constant stress drop on a circular patch expanding at 5 cm/sec over 6.5 hr. We find the slips or stress drops would have to have been implausibly high (meters or kilobars) to have been detectable on the strain meters at PFO. Slightly better limits are possible only 20 km from the source. Even though the distance from Landers to PFO is small compared with the average spacing of strain meters in California, we are unable to prove or disprove Ohnaka's model of earthquake nucleation. This suggests that even if the model is valid, it will not be useful for short-term prediction.

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Tidal influence on Rutford Ice Stream, West Antarctica: observations of surface flow and basal processes from closely spaced GPS and passive seismic stations

Journal of Glaciology ◽

10.3189/002214308786570872 ◽

2008 ◽

Vol 54 (187) ◽

pp. 715-724 ◽

Cited By ~ 29

Author(s):

G. Aðalgeirsdóttir ◽

A.M. Smith ◽

T. Murray ◽

M.A. King ◽

K. Makinson ◽

...

Keyword(s):

Tidal Cycle ◽

General Pattern ◽

Surface Flow ◽

Surface Velocity ◽

Velocity Variation ◽

West Antarctica ◽

Ice Stream ◽

Grounding Line ◽

Passive Seismic ◽

First Time

AbstractHigh-resolution surface velocity measurements and passive seismic observations from Rutford Ice Stream, West Antarctica, 40 km upstream from the grounding line are presented. These measurements indicate a complex relationship between the ocean tides and currents, basal conditions and ice-stream flow. Both the mean basal seismicity and the velocity of the ice stream are modulated by the tides. Seismic activity increases twice during each semi-diurnal tidal cycle. The tidal analysis shows the largest velocity variation is at the fortnightly period, with smaller variations superimposed at diurnal and semi-diurnal frequencies. The general pattern of the observed velocity is two velocity peaks during each semi-diurnal tidal cycle, but sometimes three peaks are observed. This pattern of two or three peaks is more regular during spring tides, when the largest-amplitude velocity variations are observed, than during neap tides. This is the first time that velocity and level of seismicity are shown to correlate and respond to tidal forcing as far as 40 km upstream from the grounding line of a large ice stream.

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In search of ice-stream sticky spots

Journal of Glaciology ◽

10.3189/s0022143000016336 ◽

1993 ◽

Vol 39 (133) ◽

pp. 447-454 ◽

Cited By ~ 7

Author(s):

Richard B. Alley

Keyword(s):

Shear Stress ◽

Large Scale ◽

Water Pressure ◽

Pressure Measurements ◽

West Antarctica ◽

Ice Surface ◽

Ice Stream ◽

Bed Roughness ◽

Basal Shear

AbstractThe basal shear stress of an ice stream may be supported disproportionately on localized regions or “sticky spots”. The drag induced by large bedrock bumps sticking into the base of an ice stream is the most likely cause of sticky spots. Discontinuity of lubricating till can cause sticky spots, but they will collect lubricating water and therefore are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps. Raised regions on the ice-air surface can also cause moderate increases in the shear stress supported on the bed beneath. Surveys of large-scale bed roughness would identify sticky spots caused by bedrock bumps, water-pressure measurements in regions of thin or zero till might reveal whether they were sticky spots, and strain grids across the margins of ice-surface highs would show whether the highs were causing sticky spots. Sticky spots probably are not dominant in controlling Ice Stream Β near the Upstream Β camp, West Antarctica.

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Persistent tracers of historic ice flow in glacial stratigraphy near Kamb Ice Stream, West Antarctica

The Cryosphere ◽

10.5194/tc-12-2821-2018 ◽

2018 ◽

Vol 12 (9) ◽

pp. 2821-2829 ◽

Cited By ~ 2

Author(s):

Nicholas Holschuh ◽

Knut Christianson ◽

Howard Conway ◽

Robert W. Jacobel ◽

Brian C. Welch

Keyword(s):

Large Scale ◽

Ross Sea ◽

Accumulation Rate ◽

Volcanic Complex ◽

West Antarctica ◽

Ice Flow ◽

Ice Stream ◽

Grounding Line ◽

Flow Pathways ◽

Kamb Ice Stream

Abstract. Variations in properties controlling ice flow (e.g., topography, accumulation rate, basal friction) are recorded by structures in glacial stratigraphy. When anomalies that disturb the stratigraphy are fixed in space, the structures they produce advect away from the source and can be used to trace flow pathways and reconstruct ice-flow patterns of the past. Here we provide an example of one of these persistent tracers: a prominent unconformity in the glacial layering that originates at Mt. Resnik, part of a subglacial volcanic complex near Kamb Ice Stream in central West Antarctica. The unconformity records a change in the regional thinning behavior seemingly coincident (∼3440±117 a) with stabilization of grounding-line retreat in the Ross Sea Embayment. We argue that this feature records both the flow and thinning history far upstream of the Ross Sea grounding line, indicating a limited influence of observed ice-stream stagnation cycles on large-scale ice-sheet routing over the last ∼ 5700 years.

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In search of ice-stream sticky spots

Journal of Glaciology ◽

10.1017/s0022143000016336 ◽

1993 ◽

Vol 39 (133) ◽

pp. 447-454 ◽

Cited By ~ 151

Author(s):

Richard B. Alley

Keyword(s):

Shear Stress ◽

Large Scale ◽

Water Pressure ◽

Pressure Measurements ◽

West Antarctica ◽

Ice Surface ◽

Ice Stream ◽

Bed Roughness ◽

Basal Shear

Abstract The basal shear stress of an ice stream may be supported disproportionately on localized regions or “sticky spots”. The drag induced by large bedrock bumps sticking into the base of an ice stream is the most likely cause of sticky spots. Discontinuity of lubricating till can cause sticky spots, but they will collect lubricating water and therefore are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps. Raised regions on the ice-air surface can also cause moderate increases in the shear stress supported on the bed beneath. Surveys of large-scale bed roughness would identify sticky spots caused by bedrock bumps, water-pressure measurements in regions of thin or zero till might reveal whether they were sticky spots, and strain grids across the margins of ice-surface highs would show whether the highs were causing sticky spots. Sticky spots probably are not dominant in controlling Ice Stream Β near the Upstream Β camp, West Antarctica.

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Stick–slip behavior of ice streams: modeling investigations

Annals of Glaciology ◽

10.3189/172756409789624274 ◽

2009 ◽

Vol 50 (52) ◽

pp. 87-94 ◽

Cited By ~ 42

Author(s):

Olga V. Sergienko ◽

Douglas R. MacAyeal ◽

Robert A. Bindschadler

Keyword(s):

West Antarctica ◽

Ice Streams ◽

Stick Slip ◽

Ice Stream ◽

Whillans Ice Stream ◽

Spatial Propagation ◽

The Difference ◽

Stick Slip Motion ◽

Transitional Phase ◽

Slip Motion

AbstractA puzzling phenomenon of ice-stream flow is the stick–slip motion displayed by Whillans Ice Stream (WIS), West Antarctica. In this study we test the hypothesis that the WIS stick–slip motion has features similar to those of other known stick–slip systems, and thus might be of the same origin. To do so, we adapt a simple mechanical model widely used in seismology to study classic stick–slip behavior observed in tectonic faults, in which the difference between static and dynamic friction allows for the generation and spatial propagation of abrupt slip events. We show how spatial variability in friction properties, as well as a periodic forcing intended to mimic the effect of tides, can reproduce the observed duration and periodicity of stick–slip motion in an ice stream. An intriguing aspect of the association of WIS with mechanical stick–slip oscillators is that the onset of stick–slip cycling from a condition of permanent slip appears to be associated with the reduction in overall speed of WIS. If this association is true, then stick–slip behavior of WIS is a transitional phase of behavior associated with the ice stream's recent deceleration.

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Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2

The Cryosphere Discussions ◽

10.5194/tcd-8-1673-2014 ◽

2014 ◽

Vol 8 (2) ◽

pp. 1673-1721 ◽

Cited By ~ 10

Author(s):

V. Helm ◽

A. Humbert ◽

H. Miller

Keyword(s):

Large Scale ◽

Ice Sheets ◽

Surface Elevation ◽

Volume Loss ◽

Radar Altimeter ◽

West Antarctica ◽

Elevation Change ◽

Amundsen Sea ◽

Ice Stream ◽

Elevation Changes

Abstract. The ESA satellite CryoSat-2 has been observing Earth's polar regions since April 2010. It carries a sophisticated radar altimeter and aims for the detection of changes in sea ice thickness as well as surface elevation changes of Earth's land and marine ice sheets. This study focuses on the Greenland and Antarctic ice sheets, considering the contemporary elevation of their surfaces. Based on 2 years of CryoSat-2 data acquisition, elevation change maps and mass balance estimates are presented. Additionally, new digital elevation models (DEMs) and the corresponding error maps are derived. Due to the high orbit of CryoSat-2 (88° N/S) and the narrow across-track spacing, more than 99% of Antarctica's surface area is covered. In contrast, previous radar altimeter measurements of ERS1/2 and ENVISAT were limited to latitudes between 81.5° N and 81.5° S and to surface slopes below 1°. The derived DEMs for Greenland and Antarctica have an accuracy which is similar to previous DEMs obtained by satellite-based laser and radar altimetry (Liu et al., 2001; Bamber et al., 2009, 2013; Fretwell et al., 2013; Howat et al., 2014). Comparisons with ICESat data show that 80% of the CryoSat-2 DEMs have an error of less than 3 m ± 30 m. For both ice sheets the surface elevation change rates between 2011 and 2012 are presented at a resolution of 1 km. Negative elevation changes are concentrated at the west and south-east coast of Greenland and in the Amundsen Sea embayment in West Antarctica (e.g. Pine Island and Thwaites glaciers). They agree well with the dynamic mass loss observed by ICESat between 2003 and 2008 (Pritchard et al., 2009). Thickening occurs along the main trunk of Kamb Ice Stream and in Dronning Maud Land. While the former is a consequence of an ice stream stagnated ∼150 years ago (Rose, 1979; Retzlaff and Bentley, 1993), the latter represents a known large-scale accumulation event (Lenaerts et al., 2013). This anomaly partly compensates for the observed increased volume loss in West Antarctica. In Greenland the findings reveal an increased volume loss of a factor of 2 compared to the period 2003 to 2008. The combined volume loss of Greenland and Antarctica for the period 2011 and 2012 is estimated to be −448 ± 122 km3 yr−1.

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