An Overview
Environmental seismology is a fairly new branch of geology, but its already improving our understanding of landscape-shaping processes. Let's take a look at the advantages (and disadvantages) of this promising field. I'll focus on recent applications in glaciers, rivers, and landslides.
What is Environmental Seismology, Anyways?
What is Environmental Seismology, Anyways?
Environmental seismology focuses on historically unwanted surface-generated vibrations. For the past century, seismologists have primarily focused on earthquakes produced by faults deep within earth, ignoring smaller vibrations produced at earth’s surface as unwanted background noise. However, recent advances in seismometer portability, sensitivity, and computation power are changing that.
A Sample of Recent Applications
Glaciers: By deploying seismometers onto glacial ice sheets, scientists are able observe glacial processes in remote areas or deep under the ice. For instance, glacial “earthquakes” are felt when icebergs break off and go into the ocean with their heavy side up. As they flip over to put the heavy side down, they can crash into the ice sheet, generating an amount of energy equivalent to up to two Hiroshima atomic bombs. The energy released produces magnitude 4-5 “earthquakes” that are detectable from thousands of miles away, but sound different than classic earthquakes caused by faulting. By counting these events and estimating their size, scientists are working to estimate the amount of ice going into the ocean from ice sheets on land (Fig. 1). This information on the rate of ice loss is needed for predictive climate models and estimating sea level rise.
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| Figure 1: Glacial earthquakes in Greenland increased during the 2000 - 2005 observation period. This could represent an increase in ice loss from Greenland into the ocean. Figure from Ekström, Nettles, and Tsai (2006). |
Rivers: River processes can be observed without ever getting wet by using near-river seismometers. Information from river-produced vibrations can also expand our understanding of how a river wears down the landscape. One of the most effective river erosion processes is thought to be the damage to bedrock done by large bedload cobbles tumbling along the bottom of a river. The rate of erosion is related to the amount of bedload. However, measuring the amount of bedload is difficult because it happens infrequently (a few times a year) and during large floods (when getting in a river is downright dangerous), so an easier and safer way to measure bedload is needed. With near-stream seismic monitoring, several researchers have been able identify bedload movement events by seeing the rumbling vibrations produced by the cobbles hitting the bottom of the river. These vibrations are different than what is produced by the water by itself, and researchers are working to try to relate the vibrations to the total amount of bedload. This research has taught us that most bedload is transported before the peak of a flood, helping to pinpoint when the most river erosion occurs (Fig. 2).
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| Figure 2: A) Seismic river observation includes both turbulent flow and bedload noise. B) Bedload transport noise is observed mostly before the peak of a flood event, suggesting river erosion is more effective during this period. Figure from Larose et al. (2015).
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Landslides: Landslides and related gravity-driven phenomena (mudslides, rockfalls, debris flows, avalanches, etc.) are hazardous and significant landscape-shaping processes that are best observed from a distance. By measuring the “sound profile” of a landslide using seismometers, scientists are working to estimate the total amount of material moved by the landslide event (Fig. 3). Emergency response agencies are interested in using this sound profile information for developing better real-time response alerts in remote areas. A widely-spread seismometer network can also be used to determine important characteristics of landslides in remote areas, including the speed, frequency of landsliding, and even the landslide trigger mechanism.
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| Figure 3: Example “sound profiles” for different sources of seismic vibrations. The left figures show the seismometer response to each event. The right figures show the frequency distribution of the events. Red on these figures is louder sounds. Note that the figures have different time domains (x axis is changing). Studying these "sound profiles" will improve natural disaster alerts in remote areas. Figure from Burtin, Hovius, and Turowski (2016). |
Evaluation of Environmental Seismology Methods
Advantages:
- Continuous Measurement: No waiting around for infrequent but significant events like iceberg calving, floods, or landslides.
- Non-Contact: Keeps scientists out of harm’s way while studying hazards
- Difficult Processes Revealed: Listening to vibrations gives new insights into the physics of landscape processes.
Disadvantages:
- Potential Interference: Road noise, precipitation, and unwanted vibrations sometimes make it difficult to focus on the process of interest, especially if it is a quiet process.
- Seismic Properties Required: Knowing about the seismic properties of the soil, rock, or ice through which the vibrations is required for this type of study, but this information is difficult to obtain.
- Non-Localized Measurement: Vibrations travel a long way, so each seismometer can be observing close by and far away processes at the same time, leading to confusion in the interpretation of signals
Looking Ahead
Environmental Seismology has already produced insights into landscape-shaping processes, and is likely to become a larger field as seismometers become cheaper, more sensitive, and easier to use. Moving forward, the field needs additional research into how each process physically produces vibrations. It also requires calibration with traditional measurement techniques. With this additional research the field will continue to develop our understanding of landscape-shaping processes.
References
Burtin, A., Hovius, N., Turowski, J. ,2016, Seismic monitoring of torrential and fluvial processes: Earth Surface Dynamics, v. 4, p. 285-307. http://doi.org/10.5194/esurf-4-285-2016
Ekström, G., Nettles, M., and Tsai, V. C., 2006, Seasonality and increasing frequency of Greenland glacial earthquakes: Science v. 311, p. 1756–1758. doi:10.1126/science.1122112
Larose, E., Carrière, S., Voisin, C., Bottelin, P., Baillet, L., Guéguen, P., Walter, F., Jongmans, D., Guillier, B., Garambois, S., Gimbert, F., Massey, C., 2015, Environmental seismology: What can we learn on earth surface processes with ambient noise?: Journal of Applied Geophysics, v. 116, p. 62-74, http://dx.doi.org/10.1016/j.jappgeo.2015.02.001.
Good introduction to this topic. You do a good job describing the fields encapsulating within environmental seismology. I also appreciate you pointing out disadvantages as well as advantages. As a geologist, I think it is easy to imagine why this field is important, but perhaps it might be useful to try and explain to general public why this field is so important to them. In short, why should they care?
ReplyDeleteP.S. Be careful not to distract the audience by pacing during your presentation.
DeleteIf you spend a bit more time during the presentation explaining how measure glacial seismic events could be used to monitor climate change you could gain a larger audience.
ReplyDeleteI think you did a good job of taking complex information and making it accessible. I also appreciate the structure you chose, particularly with regard to Advantages/Disadvantages/Looking Ahead.
ReplyDeleteI'm interested in knowing what relevance the exploding air bubbles have on data interpretation. The word explosion just caught my eye... because 'Murica.
I'm referring to Figure 2(a), btw.
DeleteWhat is the signal relative to the noise in deep Earth and surface environmental seismology? What are the properties that differentiate between deep and surface produced vibrations? Think about re-organizing this as a single narrative blog rather than a subdivided article. The title is catchy,but the information is perhaps too scientific. Perhaps consider a link to an iceberg calving event video.
ReplyDeleteIt's a very interesting topic. The three applications of environmental seismology is well explained. I'm particularly interested in the glacial part. Can you use this method to study the underground ice structure in Greenland if you put seismometers close to the icebergs?
ReplyDeleteI really enjoyed your talk and found the content really interesting. My only critique is that you say "um" quite a bit.
ReplyDeleteYou do a good job of describing the topic. I am not sure if all of that information is needed for an introduction to the topic but it is certainly thorough.
ReplyDeleteI would much rather have seen an awesome .gif of a glacier calving than a bar graph, just a suggestion!
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ReplyDeleteFor your talk, try to use fewer filler words like "um". Overall I thought you did a good job of keeping scientific terms out of the talk and article, but the visual aids were complex and not very exciting. A video or audio clip for each might be better. I am not opposed to your three-part structure, but it might be better to focus on one particular application.
ReplyDeleteYou have a good topic and are general enough for most people to catch on. I would suggest that the third figure is perhaps a bit too in-depth. The advantages and disadvantages section is quite welcome, as it draws the reader to the key points without seeming repetitive.
ReplyDeleteI really enjoyed your presentation, and amazed by how you make such a scientific topic to be so accessable. The blog is a little too scientific for my taste. But the way you use subtitles to make the structure clearly is wonderful.
ReplyDeleteI like how your post is so well organized, detailed, and thorough. I think it might benefit from an explanation of how seismometers work. Also I agree with above comments --3rd image is a a bit complicated.
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