Our guest today is Dr. Wendy Bohon, an earthquake geologist and science communicator. Although she speaks with an authority and enthusiasm that would make you think she had been doing this since the Precambrian, Dr. Bohon actually began her professional life as an actress. Living in California, she experienced the 1999 Hector Mine earthquake. This unlocked a profound interest in earthquake science, leading to her PhD in Geology, and current role as Senior Science Communication Specialist for the Incorporated research Institutions for Seismology where she furthers her mission of educating the public on how earthquake geology can affect them.
Mapping Earthquake Geology
Before diving too deep into our earth, it’s important to first build a foundation of terminology. Two frequently merged concepts are earthquake geology, and seismology. They do come up in the same conversations, but are unique studies.
Earthquake geology focuses on the impacts to the surface of our earth. This involves understanding the form and structure of the crust, and how faults and the surface change as a result of repeated earthquakes.
Seismology is the study of seismic waves and taking a deeper look inside the earth. Seismologists use seismometers or geophones to measure movement under the surface. These instruments can even detect tornadoes and hurricanes above ground. There are two sources of seismology. Passive sources are natural movement, like from earthquakes, or artificial movement, like from construction or other surface activity. Active source seismology is a result of induced seismic waves. This can be from explosives, air bursts for underwater testing, or the classic combination of some metal plates and a sledgehammer.
So why are so many people involved and invested in answering geological questions with GIS and geographic methods? Well, as the saying goes, “ What gets measured gets managed”.
Creating a more complete map of the earth’s mineral resources provides a better foundation for planning for future extraction, conservation, and risk management.
Knowing areas of higher risk allows communities to plan accordingly, and communicate potential hazards to their citizens.
Considering that the very nature of earthquakes and seismology require understanding and documenting change, maps are essential for coming to significant conclusions. Scientists employ a number of geospatial tools, such as GNSS systems and remote sensing, to better document the earth’s makeup.
These techniques will often be combined with more traditional geologic methods, like taking ground samples, in order to verify findings and better tune standards and signatures for digital sampling.
The Role of GPS in Geology
GNSS technology, whether it takes the form of GPS (USA), GLONASS (Russia), BeiDou (China) or Galileo (EU), has far more uses and applications than we have generally given it credit for. There is of course huge value in knowing exactly where the device is on the earth, but what if we could capture information on the surrounding area as well?
Following the standard use of GPS, there are a lot of things that geologists can learn about the planet’s changes. Primarily, they are interested in movement. By taking readings with a device at a fixed location over a long period of time, a technique known as campaign GPS, the scientist can get finely detailed measurements of vertical and horizontal movement. Changes in the device’s location are interpreted as movement.
In order to translate movement to meaning, the trained eye of a geologist is needed. Observing two GPS units positioned on the opposite sides of a fault line, they can determine the expected rate of movement of that fault.
If the observer notices one year that the movement is outside of the expected range, then that is an indicator there may be an earthquake on the way.
Although more is better, if a scientist is working with only one GPS unit, they can still get useful scientific information. A unit placed on a volcano can help give information on if the surface is bulging or shifting, indicating a possible future eruption.
Outside of the common application of simply measuring location, GPS units and their signals can be used more creatively to paint a better picture of the landscape.
Multipath error is the result of a GPS unit giving or receiving conflicting or reflected signals due to the surrounding environment.
Traditionally, multipath error is accounted for and thrown out as just that, error. If a researcher is willing to sift through the noise, however, it is possible to get an estimate of the changes in height of the surrounding environment by categorizing some of the recurring errors. These height differences and changes can be interpreted as snow depth, or growth in vegetation, depending on the study area’s geography.
Geology and Remote Sensing
Considering that nowhere on earth can we escape geology, it makes sense to take science to the sky to better understand and measure it. By using satellites, drones, UAVs, and the many sensors and scanners that can be attached to them, geologists are able to make observations on a much larger scale more efficiently than if they were restricted to the ground.
Lidar is especially useful as it allows for repeatable construction of a digital terrain model (DTM) that exposes the shape of the ground below tree canopies.
This is great for seismologically active areas with heavy forest cover, such as the Pacific Northwest of the United States. A detailed 3D representation of the surface can show features associated with faults, allowing for a better geological inventory of the area.
Of course, more traditional sensors play a great role in geology as well. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a fantastic resource for geologists as it hosts visible and near infrared (VNIR), short wave infrared (SWIR), and thermal infrared (TIR) sensors.
These infrared bands are useful for studying the mineral makeup of the earth as different minerals will have different spectral signatures. By understanding the mineral content of the surface, it is possible to infer the types of rocks present, as rocks are simply collections of minerals. Once a geologist knows what rocks are present on the surface, this can allow them to make educated assessments of the bedrock of the area.
The earth is of course not static, but rather a living, and even breathing force. The more we invest into understanding and mapping all the nuances and features of our planet, the more prepared we will be when it comes time to take action against some of the world’s most pressing challenges.