Search for: All records

Abstract Seismic imaging in 3-D holds great potential for improving our understanding of ice sheet structure and dynamics. Conducting 3-D imaging in remote areas is simplified by using lightweight and logistically straightforward sources. We report results from controlled seismic source tests carried out near the West Antarctic Ice Sheet Divide investigating the characteristics of two types of surface seismic sources, Poulter shots and detonating cord, for use in both 2-D and 3-D seismic surveys on glaciers. Both source types produced strong basal P-wave and S-wave reflections and multiples recorded in three components. The Poulter shots had a higher amplitude for low frequencies (<10 Hz) and comparable amplitude at high frequencies (>50 Hz) relative to the detonating cord. Amplitudes, frequencies, speed of source set-up, and cost all suggested Poulter shots to be the preferred surface source compared to detonating cord for future 2-D and 3-D seismic surveys on glaciers. 

ABSTRACT In September 2017, over 450 lives were lost in Mexico as a result of two unusual, large-magnitude, normal earthquakes. On 7 September, an M 8.2 earthquake occurred offshore of the State of Oaxaca in the Gulf of Tehuantepec, one of the largest extensional earthquakes to have occurred in a subduction zone. Twelve days later on 19 September an M 7.1 damaging earthquake struck near Puebla and Morelos, over 600 km away. Both earthquakes occurred in the downgoing Cocos plate, which is subducting beneath the North American plate. The first large event was followed on 23 September by a shallow M 6.1 extensional earthquake near Juchitán de Zaragoza, Oaxaca. Researchers from Mexico and the United States collaborated to deploy a temporary seismic network to study the aftershocks of the M 8.2 Tehuantepec, Mexico, earthquake, which included a three-week deployment of 51 Magseis Fairfield Z-Land 5-Hz three-component nodal seismometers (“nodes”) near Juchitán and a 6-month deployment of 10 Nanometrics Trillium 120PA broadband seismometers with Reftek RT130 dataloggers for 6 months. In this article, we analyze the capabilities of the nodes to calculate the horizontal/vertical (H/V) spectral ratio and relative amplification using both microtremors and earthquakes and validate the results calculated with the nodes using data from broadband stations from this and previous deployments in the area. We create maps showing a correlation of the distribution of the fundamental frequency and relative amplification of the soil and compare them with the geology and the damage caused by the September 2017 earthquakes. There is a lack of public awareness and discrepancies in the construction procedures in the region, and we find that the majority of damaged houses in the area of study followed the location of river beds and tended to be in places with low resonance frequencies despite being in a low amplification zone. 

Abstract To increase inclusivity, diversity, equity and accessibility in Antarctic science, we must build more positive and inclusive Antarctic field work environments. The International Thwaites Glacier Collaboration (ITGC) has engaged in efforts to contribute to that goal through a variety of activities since 2018, including creating an open-access ‘Field and Ship Best Practices’ guide, engaging in pre-field season team dynamics meetings, and surveying post-field season reflections and experiences. We report specific actions taken by ITGC and their outcomes. We found that strong and supported early career researchers brought new and important perspectives regarding strategies for transforming culture. We discovered that engaged and involved senior leadership was also critical for expanding participation and securing funding to support efforts. Pre-field discussions involving all field team members were particularly helpful for setting expectations, improving sense of belonging, describing field work best practices, and co-creating a positive work culture. 

Steamboat Geyser in Yellowstone National Park’s Norris Geyser Basin began a prolific sequence of eruptions in March 2018 after 34 y of sporadic activity. We analyze a wide range of datasets to explore triggering mechanisms for Steamboat’s reactivation and controls on eruption intervals and height. Prior to Steamboat’s renewed activity, Norris Geyser Basin experienced uplift, a slight increase in radiant temperature, and increased regional seismicity, which may indicate that magmatic processes promoted reactivation. However, because the geothermal reservoir temperature did not change, no other dormant geysers became active, and previous periods with greater seismic moment release did not reawaken Steamboat, the reason for reactivation remains ambiguous. Eruption intervals since 2018 (3.16 to 35.45 d) modulate seasonally, with shorter intervals in the summer. Abnormally long intervals coincide with weakening of a shallow seismic source in the geyser basin’s hydrothermal system. We find no relation between interval and erupted volume, implying unsteady heat and mass discharge. Finally, using data from geysers worldwide, we find a correlation between eruption height and inferred depth to the shallow reservoir supplying water to eruptions. Steamboat is taller because water is stored deeper there than at other geysers, and, hence, more energy is available to power the eruptions. 

Abstract Understanding the dynamic response of glaciers to climate change is vital for assessing water resources and hazards, and subglacial hydrology is a key player in glacier systems. Traditional observations of subglacial hydrology are spatially and temporally limited, but recent seismic deployments on and around glaciers show the potential for comprehensive observation of glacial hydrologic systems. We present results from a high‐density seismic deployment spanning the surface of Lemon Creek Glacier, Alaska. Our study coincided with a marginal lake drainage event, which served as a natural experiment for seismic detection of changes in subglacial hydrology. We observed glaciohydraulic tremor across the surface of the glacier that was generated by the subglacial hydrologic system. During the lake drainage, the relative changes in seismic tremor power and water flux are consistent with pressurization of the subglacial system of only the upper part of the glacier. This event was not accompanied by a significant increase in glacier velocity; either some threshold necessary for rapid basal motion was not attained, or, plausibly, the geometry of Lemon Creek Glacier inhibited speedup. This pressurization event would have likely gone undetected without seismic observations, demonstrating the power of cryoseismology in testing assumptions about and mapping the spatial extent of subglacial pressurization.