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3-D CT Core Imaging Laboratory

Learn more about the Rotating X-ray Computed Tomography (RXCT) system at the USGS Pacific Coastal and Marine Science Center in Santa Cruz, California.

Photograph of a laboratory with a big x-ray machine and two computers for calibration and visualization.
The Geotek RXCT, a rotating x-ray computed tomography system, is used for creating ultra high-resolution imagery of sediment cores. The system resides at the USGS Pacific Coastal and Marine Science Center in Santa Cruz, California. It requires the operator to take specialized training and hold safety certifications.

The Geotek RXCT, a "rotating x-ray computed tomography" system, creates ultra high-resolution imagery of sediment cores. The system resides at the USGS Pacific Coastal and Marine Science Center in Santa Cruz, California. It requires the operator to take specialized training and hold X-ray radiation and safety certifications.

In medicine, radiologists use computed tomography (CT) scans to collect highly detailed images of your body. Similarly, the RXCT creates a complete 3-D image rendering of a sediment core by combining a series of X-ray images taken from different angles around it (thus, the "rotating" part of the name). The system then uses computer processing to create cross-sectional images (slices) of the core. Thus, a CT scan provides more detailed information than a simple 2-D X-ray image.

The images created by the RXCT allow scientists to look into the core at any area and at any angle, without having to carve into it. Looking at the structure and composition of cores in this fashion helps scientists determine the history of the location where the core was collected, such as the seafloor, a lake bed, or a marshy area. For example, if they find a sandy layer in an otherwise calm environment, like a coastal marsh which is normally just peat and mud, this may be evidence of a big wave event that carried sand from the beach and nearshore back into the marsh area. Further inspection of the CT image may reveal subtle sedimentary characteristics of the sandy deposit such as changes in grainsize, heavy mineral layers, and rip-up clasts that may help researchers determine whether deposition occurred during a tsunami or a storm.

 

Various images of a long and narrow core of sediment that show various features within the sediment.
Images from a sediment core taken from Floras Lake, a coastal lake in southern Oregon. At the far left is a false color computed tomography (CT) scan of a sediment core, and next to it is an actual photograph of the core. The box shows the area of an expanded, zoomed-in section of these images, which is displayed in the center. In both the CT scan and the photograph, the lighter, brighter colors are dense sand and the darker colors are mud layers. At far right is another false color image of the CT scan. Scientists use the CT scan in order to see unique aspects of the layers of sediment that may otherwise not be visible.
A view of a thin slab of sediment as if cut from a core, the image rotates around to show front and back and internal structure.
False color CT scan of a core from Floras Lake, a coastal lake in southern Oregon that contains a record of tsunamis going back at least 6700 years. The beige (light) color is sand, which is more dense than the mud (brown, dark) surrounding it. As the animation continues, the darker colors are hidden in order to highlight the lighter colors of the sand deposits. This helps scientists see amazing detail to help them form the sedimentologic "story" about how the sand was deposited. The oval fragments of mud in the upper part of the sandy deposit appear to be rip-up clasts, indicative of an erosive, high flow into the lake that deposited beach and dune sand in the basin. This particular deposit is about 8 cm thick, and radiocarbon dating of sediments above and below the sand suggest that the tsunami was generated by a Cascadia megathrust earthquake roughly 2000 years ago.
An offshore map shows location of ocean exploration and a star where a sediment core was collected, with photos of the core.
The figure shows the location of remotely operated vehicle (ROV) Doc Ricketts dives conducted in September 2020, plus three images of the CT scan data from one of the collected cores. The ROV is operated by Monterey Bay Aquarium Research Institute (MBARI) from the research vessel (R/V) Western Flyer. The USGS Pacific Coastal and Marine Science Center in Santa Cruz regularly collaborates with MBARI, and most recently the USGS and MBARI efforts center around the study of the Cascadian Margin, a subduction zone off CA, OR, and WA. The figure includes a photograph of a vertical slice through the upper 80 cm of the core "DR1281 VC-870," with a zoomed in section to the right, outlined in red. Lighter colors indicate sandy sediment and suggest horizons associated with 4 turbidites. In the lower right is a perpendicular slice through a horizon (its location is marked as an orange line through the zoomed-in cross-section) showing coarse grains that are characteristic of turbidites. Previously published work identified a sand layer in a core at this same site and subbottom depth, which was determined to be associated with the January 1700 Cascadia mega-earthquake and subsequent tsunami.

News

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Searching for Evidence of Past Tsunamis in Sediment Cores

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New evidence for a roughly 600-year-old tsunami impacting the Hawaiian Islands

Publications

Rebounds, regresses, and recovery: A 15-year study of the coral reef community at Pila‘a, Kaua‘i after decades of natural and anthropogenic stress events

Pila‘a reef on the north shore of Kaua‘i, Hawai‘i was subjected to a major flood event in 2001 that deposited extensive sediment on the reef flat, resulting in high coral mortality. To document potential recovery, this study replicated benthic and sediment surveys conducted immediately following the event and 15 years later. Coral cores were analyzed to determine coral growth rates and density. Ou

Bomb-produced radiocarbon across the South Pacific Gyre — A new record from American Samoa with utility for fisheries science

Coral skeletal structures can provide a robust record of nuclear bomb produced 14C with valuable insight into air-sea exchange processes and water movement with applications to fisheries science. To expand these records in the South Pacific, a coral core from Tutuila Island, American Samoa was dated with density band counting covering a 59-yr period (1953–2012). Seasonal signals in elemental ratio

Coral skeleton δ15N as a tracer of historic nutrient loading to a coral reef in Maui, Hawaii

Excess nutrient loading to nearshore environments has been linked to declining water quality and ecosystem health. Macro-algal blooms, eutrophication, and reduction in coral cover have been observed in West Maui, Hawaii, and linked to nutrient inputs from coastal submarine groundwater seeps. Here, we present a forty-year record of nitrogen isotopes (δ15N) of intra-crystalline coral skeletal organi

Science

Cascadia Subduction Zone Marine Geohazards

Societal Issue: Uncertainty related to rupture extent, slip distribution, and recurrence of past subduction megathrust earthquakes in the Pacific Northwest (northern CA, OR, WA, and southern BC) leads to ambiguity in earthquake and tsunami hazard assessments and hinders our ability to prepare for future events.
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Cascadia Subduction Zone Marine Geohazards

Societal Issue: Uncertainty related to rupture extent, slip distribution, and recurrence of past subduction megathrust earthquakes in the Pacific Northwest (northern CA, OR, WA, and southern BC) leads to ambiguity in earthquake and tsunami hazard assessments and hinders our ability to prepare for future events.
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Hazards: EXPRESS

Marine geohazards including earthquakes, landslides, and tsunamis lie offshore of densely populated areas of California, Oregon, and Washington. One goal of EXPRESS is to improve assessments of these hazards.
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Hazards: EXPRESS

Marine geohazards including earthquakes, landslides, and tsunamis lie offshore of densely populated areas of California, Oregon, and Washington. One goal of EXPRESS is to improve assessments of these hazards.
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U.S. West Coast and Alaska Marine Geohazards

Marine geohazards are sudden and extreme events beneath the ocean that threaten coastal populations. Such underwater hazards include earthquakes, volcanic eruptions, landslides, and tsunamis.
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U.S. West Coast and Alaska Marine Geohazards

Marine geohazards are sudden and extreme events beneath the ocean that threaten coastal populations. Such underwater hazards include earthquakes, volcanic eruptions, landslides, and tsunamis.
Learn More