First detailed 3-D images of a megathrust fault show long grooves and other features in the fault surface that are likely to control how it slips in an earthquake
Geophysicists have obtained detailed three-dimensional images of a dangerous megathrust fault west of Costa Rica where two plates of the Earth's crust collide. The images reveal features of the fault surface, including long grooves or corrugations, that may determine how the fault will slip in an earthquake.
The study, published February 12 in Nature Geoscience, focused on the Costa Rica subduction zone where the Cocos plate slowly dives beneath the overriding Caribbean plate. Variations in texture seen in different portions of the fault surface may explain why Costa Rica has complex, patchy earthquakes that do not seem to slip to shallow depths, unlike some other megathrust faults, said first author Joel Edwards, a Ph.D. candidate in Earth and planetary sciences at UC Santa Cruz.
"Our new imagery shows large variability in the conditions along the megathrust, which may be linked to a number of earthquake phenomena we observe in the region," Edwards said.
Megathrusts, the huge continuous faults found in subduction zones, are responsible for Earth's largest earthquakes. Megathrust earthquakes can generate destructive tsunamis and are a serious hazard facing communities located near subduction zones. Understanding the mechanisms at work along these faults is vital for disaster management around the globe.
Edwards worked with a team of geophysicists at UC Santa Cruz, the U.S. Geological Survey, the University of Texas-Austin, and McGill University to obtain 3-dimensional imagery of the fault interface using cutting-edge acoustic imaging technology. The long grooves, or corrugations, they observed along the interface are similar in size to those found along the base of fast-flowing glaciers and along some ocean ridges. The images also showed varying amounts of smoothness and corrugations on different portions of the fault.
"This study produced an unprecedented view of the megathrust. Such 3-D information is critical to our ability to better understand megathrust faults and associated hazards worldwide," said coauthor Jared Kluesner, a geophysicist at the USGS in Santa Cruz.
The acoustic dataset was collected in spring 2011 on the academic research vessel Marcus G. Langseth. The ship towed an array of underwater microphones and sound sources behind it as it made a series of overlapping loops over the area of the fault. The data were processed over the next 2 years and have since been used in a number of studies looking at different aspects of the subduction zone process. This particular study focused on the interface between the sliding plates, which serves as a record of slip and slip processes.
"The 3-D site selection was really good and the resulting acoustic dataset showed extraordinary detail," said Edwards, noting that coauthor Emily Brodsky, professor of Earth and planetary sciences, was the first to recognize the corrugations. Such features had been observed in exposed faults on land, but never before in a fault deep beneath the surface.
"I had an early rendition of the interface that vaguely showed long grooves, and during my qualifying exam, Brodsky saw them and asked, 'are those corrugations!?' I didn't know, but I knew they were real features. Slip-derived corrugations was a really neat hypothesis, and we dug into it after that," he said.
The area in this study had long been a target for drilling into the megathrust by the Costa Rica Seismic Project (CRISP). Coauthor Eli Silver, professor emeritus of Earth and planetary sciences at UC Santa Cruz, and others in the CRISP program decided to pursue a 3-D seismic study, which must precede any deep drilling, and the project was funded by the National Science Foundation in 2009. "At present, two drilling expeditions have been accomplished with shallower targets, and, though not yet scheduled, we are hopeful that the deep drilling will occur," Silver said.
Researchers hope to use similar imaging techniques on other subduction zones, such as the Cascadia margin along the northern U.S. west coast, where there is a long history of large megathrust earthquakes and related tsunamis. "Conducting this type of 3-D study along the Cascadia margin could provide us with key information along the megathrust, a plate boundary that poses a substantial hazard risk to the U.S. west coast," Kluesner said.
In addition to Edwards, Kluesner, Silver, and Brodksy, the coauthors of the paper include Danny Brothers at the USGS; Nathan Bangs at University of Texas, Austin; Jamie Kirkpatrick at McGill University; and Ruby Wood and Kristina Okamoto, both undergraduates at UC Santa Cruz.
Tim Stephens | EurekAlert!
AWI researchers measure a record concentration of microplastic in arctic sea ice
24.04.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Climate change in a warmer-than-modern world: New findings of Kiel Researchers
24.04.2018 | Christian-Albrechts-Universität zu Kiel
Magnetic resonance imaging, or MRI, is a widely used medical tool for taking pictures of the insides of our body. One way to make MRI scans easier to read is...
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
26.04.2018 | Power and Electrical Engineering
26.04.2018 | Life Sciences
26.04.2018 | Power and Electrical Engineering