Michael K. McCarter

Massive landslide at Utah copper mine generates wealth of geophysical data

On the evening of 10 April 2013 (MDT) a massive landslide occurred at the Bingham Canyon copper mine near Salt Lake City, Utah, USA. The northeastern wall of the 970-m-deep pit collapsed in two distinct episodes that were each sudden, lasting ~90 seconds, but separated in time by ~1.5 hours. In total, ~65 million cubic meters of material was deposited, making the cumulative event likely the largest non-volcanic landslide to have occurred in North America in modern times. Fortunately, there were no fatalities or injuries. Because of extensive geotechnical surveillance, mine operators were aware of the instability and had previously evacuated the area. The Bingham Canyon mine is located within a dense regional network of seismometers and infrasound sensors, making the 10 April landslide one of the best recorded in history. Seismograms show a complex mixture of shortand long-period energy that is visible throughout the network (6–400 km). Local magnitudes (M L ) for the two slides, which are based on the amplitudes of short-period waves, were estimated at 2.5 and 2.4, while magnitudes based on the duration of seismic energy (m d ) were much larger (>3.5). This magnitude discrepancy, and in particular the relative enhancement of longperiod energy, is characteristic of landslide seismic sources. Interestingly, in the six days following the landslide, 16 additional seismic events were detected and located in the mine area. Seismograms for these events have impulsive arrivals characteristic of tectonic earthquakes. Hence, it appears that in this case the common geological sequence of events was inverted: Instead of a large earthquake triggering landslides, it was a landslide that triggered several small earthquakes.

Coal-Mining Seismicity and Ground-Shaking Hazard: A Case Study in the Trail Mountain Area, Emery County, Utah

We describe a multipart study to quantify the potential ground-shaking hazard to Joes Valley Dam, a 58-m-high earthfill dam, posed by mining-induced seismicity (mis) from future underground coal mining, which could approach as close as ∼1 km to the dam. To characterize future mis close to the dam, we studied mis located ∼3–7 km from the dam at the Trail Mountain coal mine. A 12-station local seismic network (11 stations above ground, one below, combining eight triaxial accelerometers and varied velocity sensors) was operated in the Trail Mountain area from late 2000 through mid-2001 for the dual purpose of (1) continuously monitoring and locating mis associated with longwall mining at a depth of 0.5–0.6 km and (2) recording high-quality data to develop ground-motion prediction equations for the shallow mis. (Ground-motion attenuation relationships and moment-tensor results are reported in companion articles.) Utilizing a data set of 1913 earthquakes ( M ≤ 2.2), we describe space-time-magnitude distributions of the observed mis and source-mechanism information. The mis was highly correlated with mining activity both in space and time. Most of the better-located events have depths constrained within ±0.6 km of mine level. For the preponderance (98%) of the 1913 located events, only dilatational P -wave first motions were observed, consistent with other evidence for implosive or collapse-type mechanisms associated with coal mining in this region. We assess a probable maximum magnitude of M 3.9 (84th percentile of a cumulative distribution) for potential mis close to Joes Valley Dam based on both the worldwide and regional record of coal-mining-related mis and the local geology and future mining scenarios.

Changes in mining‐induced seismicity before and after the 2007 Crandall Canyon Mine collapse

On 6 August 2007, the Crandall Canyon Mine in central Utah experienced a major collapse that was recorded as an Mw 4.1 seismic event. Application of waveform cross-correlation detection techniques to data recorded at permanent seismic stations located within ~30 km of the mine has resulted in the discovery of 1494 previously unknown microseismic events related to the collapse. These events occurred between 26 July 2007 and 19 August 2007 and were detected with a magnitude threshold of completeness of 0.0, about 1.6 magnitude units smaller than the threshold associated with conventional techniques. Relative locations for the events were determined using a double-difference approach that incorporated absolute and differential arrival times. Absolute locations were determined using ground-truth reported in mine logbooks. Lineations apparent in the newly detected events have strikes similar to those of known vertical joints in the mine region, which may have played a role in the collapse. Prior to the collapse, seismicity occurred mostly in close proximity to active mining, though several distinct seismogenic hot spots within the mine were also apparent. In the 48 h before the collapse, changes in b value and event locations were observed. The collapse appears to have occurred when the migrating seismicity associated with direct mining activity intersected one of the areas identified as a seismic hot spot. Following the collapse, b values decreased and seismicity clustered farther to the east.

Magnitude‐based discrimination of man‐made seismic events from naturally occurring earthquakes in Utah, USA

We investigate using the difference between local (ML) and coda/duration (MC) magnitude to discriminate manmade seismic events from naturally occurring tectonic earthquakes in and around Utah. For 6,846 well-located earthquakes in the Utah region, we find that ML-MC is on average 0.44 magnitude units smaller for mining induced seismicity (MIS) than for tectonic seismicity (TS). Our interpretation of this observation is that MIS occurs within near-surface low-velocity layers that act as a waveguide and preferentially increase coda duration relative to peak amplitude, while the vast majority of TS occurs beneath the near-surface waveguide. A second dataset of 3,723 confirmed or probable explosions in the Utah region also has significantly lower ML-MC values than TS, likely for the same reason as the MIS. These observations suggest that ML-MC is useful as a depth indicator and could discriminate small explosions and mining-induced earthquakes from deeper, naturally occurring earthquakes at local-to-regional distances.

Processing of terfenol-d alloy based magnetostrictive composites by dynamic compaction

Composites of Terfenol-D with metal binders were produced by explosive compaction. Compacts produced from powders prepared this way had a soft phase and intimate contact and bonding between particles are achieved. M/sub s//volume follows the expected trend based on the separate M/sub s//volume values of the constituents added. Magnetostriction of compacts made from mixture of Cu coated terfenol-D powder and Cu powder at a compressive stress of about 18 MPa were 110/spl times/10/sup -6/ and 195/spl times/ 10/sup -6/ prior to and after stress relief anneal at 350/spl deg/C. This value is about 18% of that obtained with Terfenol-D. Magnetic alignment of the powder during compaction can increase this to levels obtained in Terfenol-D-polymer composites. These composites had Youngs moduli values in the range of 33-36 GPa and were strong and tough enough to withstand machining operation.

Acoustic emission and changes in dislocation structure and magnetostriction accompanying plastic deformation of [126]-oriented Fe-Ga alloy single crystals

Controlled compressive deformation of [126]-oriented Fe-20 at. % Ga alloy single crystal along [126] direction results in large and asymmetric changes in the magnetostriction of the sample. This is in contrast to a much smaller change in magnetostriction observed in [100]-oriented single crystal deformed along [001] direction. Deformation of [126]-oriented crystal along [126] direction involved operation of only one of the slip systems. This is confirmed by TEM examination that showed only a single set of dislocation array which introduces asymmetric strain modulation in the crystal. The [100]-oriented crystal deformation involved operation of multiple slip systems and formation of several sets of dislocation arrays which introduce more symmetric strain modulations. The results suggest that the nature of strain modulation introduced by the dislocation arrays has a strong influence on the magnetostrictive behavior. Several sudden load drops accompanied by acoustic emissions and formation of slip bands were observed during [126]-oriented crystal deformation, while no such load drops or audible acoustic emissions were seen during the [001]-oriented crystal deformation.

Effect of hydrogen and magnetic field on the mechanical behavior of high strength AISI 4340 steel

Presence of hydrogen in materials is known to affect their mechanical properties due to hydrogen embrittlement problem. Steels used in various applications are prone to be exposed to aqueous electrochemical environments, which may introduce hydrogen into the alloy. These alloys are also prone to be simultaneously exposed to magnetic field, which may affect the hydrogen embrittlement susceptibility of these alloys. Therefore, it is important to examine the effect of hydrogen and magnetic field on the mechanical behavior of iron-based alloys. In this work, the effect of hydrogen and magnetic field on the fracture behavior of high strength AISI 4340 steel was examined. Three-point bend test was used to study the fracture behavior. In all the cases, the samples tested with hydrogen charging show a drastic reduction in ductility and fracture stress values. The effect of magnetic field was seen to be negligible. The hydrogen embrittlement was characterized by a change in the fracture surface from a ductile-type fracture to a brittle cleavage-type fracture. Acoustic emission signals collected during the test corresponds to the fracture behavior.