| Tuesday Mar 04, 2025 5:30 PM - Tuesday Mar 04, 2025 8:00 PM | Free - $25.00 |
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Event
AEG Nisqually March Meeting -
AEG Nisqually Dinner Meeting, March 4thMegan Anderson, Ph.D., Washington Geological Survey
When:
Tuesday, March 4th, 2025 **Please note earlier times**- 5:30 pm - Social hour and buffet dinner
- 6:30 pm - Talk
- 7:30 pm - Brief Q&A
Where:
Mercato Ristorante (in the Wine Room)
111 Market St NE, Olympia, WA 98501
Google maps link: https://maps.app.goo.gl/iW4YZTFnhKFeg21B6
Admission includes dinner and the presentation. The price is $25 for professionals, $15 for educators & job seekers, and $5 for students.
Speaker: Megan Anderson, Ph.D.
Talk Title:
Deep Structure of Siletzia: Why the middle of the crust matters for engineering seismology
Abstract:
Detailed understanding of crustal components and tectonic history of forearcs is important due to their geological complexity and high seismic hazard. The principal component of the Cascadia forearc is Siletzia, a composite basaltic terrane of oceanic origin. Much is known about the lithology and age of the province. However, glacial sediments blanketing the Puget Lowland obscure its lateral extent and internal structure, hindering our ability to fully understand its tectonic history and its influence on modern deformation. In this study, we apply map-view interpretation and two-dimensional modeling of aeromagnetic and gravity data to the magnetically stratified Siletzia terrane revealing its internal structure and characterizing its eastern boundary. These analyses suggest this boundary dips east where it crosses the Kingston arch, while south of Seattle the contact dips west where it crosses the Seattle uplift. Elongate pairs of high and low magnetic anomalies over the Seattle uplift suggest imbrication of steeply-dipping, deeply-rooted slices of Crescent Formation within Siletzia. We hypothesize these features result from duplication of Crescent Formation in an accretionary fold-thrust belt during the Eocene. The active Seattle fault divides this Eocene fold-thrust belt into two zones with different structural trends and opposite frontal ramp dips, suggesting the Seattle fault may have originated as a tear fault during accretion. Similar analyses of southwestern Washington suggest the mid-to lower crust contains a block of ultramafic material (an Eocene-age volcanic center?) that is deforming differently than the surrounding parts of Siletzia. Together, the correlation of seismicity with the block edges and recent structural modeling of the Tacoma basin give new hypotheses for seismic hazard of southwest Washington, including the Olympia fault.
Biography:
Megan Anderson is an earthquake geophysicist at the Washington Geological Survey. Megan spent her early years in Kent, WA during which the eruption of Mt. St. Helens spurred her fascination with geology, which was her major at Carleton College in Minnesota. She studied subduction seismology in South America for her Ph.D. at the University of Arizona, including investigating questions about subducting slab dynamics and overriding plate deformation in thick-skinned orogenic belts. Megan got her start studying neotectonics in the Pacific Northwest during her Mendenhall Postdoc with the USGS in Menlo Park, CA. She taught for 10 years at Colorado College, in Colorado Springs and there studied numerous tectonic regions of the world but always made her way back to the Pacific Northwest because there is so much left to discover. Megan now works to extend our understanding of active crustal faulting in Washington State and promote earthquake safety for Washington citizens.
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LocationMercato Ristorante (View)
111 Market St NE
OLYMPIA, WA 98501
United States
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| Kid Friendly: No |
| Dog Friendly: No |
| Non-Smoking: Yes! |
| Wheelchair Accessible: Yes! |
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