University of Puget Sound Sound Ideas

Summer Research

Summer 2014 Location and Classification of the Olympia Structure, Olympic Peninsula, WA Jackie Perkins University of Puget Sound, [email protected]

Follow this and additional works at: http://soundideas.pugetsound.edu/summer_research Part of the Geology Commons, Geophysics and Seismology Commons, and the Tectonics and Structure Commons

Recommended Citation Perkins, Jackie, "Location and Classification of the Olympia Structure, Olympic Peninsula, WA" (2014). Summer Research. Paper 224. http://soundideas.pugetsound.edu/summer_research/224

This Article is brought to you for free and open access by Sound Ideas. It has been accepted for inclusion in Summer Research by an authorized administrator of Sound Ideas. For more information, please contact [email protected]. Location and Classification of the Olympia Structure, Olympic Peninsula, WA Jacklyn Perkins, Ken Clark, Mike Valentine Geology Department, University of Puget Sound, Tacoma, WA

Abstract Results

A Day 1 The Olympia Structure, a major regional structure only recently recognized in the Puget Sound, Day 4 Day 3 Day 2 could be either a thrust fault or a compressional fold. Aeromagnetic studies (Fig. 1) have matched Bridge a large magnetic anomaly to the Olympia Structure, which we speculate to lie in Vance Creek. Ground surveys were conducted measuring changes in gravity and magnetism in order to pinpoint the Olympia Structure’s location and decipher its geologic significance.

Introduction and Research Questions

Aeromagnetic Anomalies, B C Shelton Quadrangle Day 2 Day 1 Compressional forces result in a number of thrust 123°30´ 123°15´ 123° 47°30´ faults (Fig. 2) in the Puget Sound Lowlands and 47°30´ nT

900 on the Olympic Peninsula. Aeromagnetic data 800 700 600 500 from Tabor, et al (1999) shows a sharp, linear 400 300 200 100 anomaly just south of the Hood Canal, known as 0 -100 -200 -300 the Olympia Structure (Fig. 1). There is -400 -500 uncertainty about whether this represents a fault

47°15´ 47°15´ or a fold. This research aims to: Figure 5. Map of D E

Shelton Day 2 Day 1 • Precisely locate the Olympia Structure and Contours of equal traverses within magnetic intensity

Shoreline

• Classify the structure either as a thrust fault or Major highway the study area. Secondary road a fold City or town Image taken from Figure 2. Major faults Google Earth of Puget Sound. O= (Accessed August 47° 47° 123°30´ 123°15´ 123° 29, 2014), map Olympia, T=Tacoma, This map shows aeromagnetic anomalies of the Shelton, Washington, 30' by 60' quadrangle. The map is based on a 1997 aeromagnetic survey of the 0 5 10 15 20 25 KM entire Puget Sound, described in U.S. Geological Surv ey Open-File Report 99-514 and available on the Internet at http://geopubs.wr.usgs.gov/open- file/of99-514. The digital version of this map was produced at 1:100,000 scale. Dimensional calibration may vary between electronic plotters and taken from USGS. between X and Y directions on the same plotter, and paper may change size HC=Hood Canal, due to atmospheric conditions; therefore, scale and proportions may not be true on plots of this map. dashed lines mark Figure 1. Aeromagnetic survey of the *Gravity data collection for Figure 4(A-E). Magnetic (A, B, C) and gravity (D, E) data collected over approximate Traverse 1 was halted by region of interest, modified from Tabor, et three traverses transecting Vance Creek. locations. Taken from regional fires. al (1999). Black arrow identifies the linear Johnson, et al (1999). anomaly of focus. Conclusions Data Collection and Analysis Large anomalies in the magnetic surveys suggest a subsurface structure underlying Vance Creek. The gravity data collected does not indicate an obvious structure, though collection is Data collection utilized not yet complete. The correspondence of the aeromagnetic map(s) of Puget Sound with the A B • LaCoste-Romberg spring magnetic data collected in this research provide strong evidence for the presence of the gravimeter Olympia Structure in Vance Creek. • Model G-856 portable proton precession magnetometer • Garmin GPSmap 62 Future Research Future Research Data point intervals This project will continue with gravity data collection for Traverse 1 along with additional • Magnetometer: 10 ft magnetic and gravity surveys. Analysis of lithological inconsistencies throughout the study area • Gravimeter: 100 ft will also provide evidence toward the classification of the Olympia Structure.

Corrections Figure 3. A) Location of study area, modified from WA Gap • Magnetism: none Project (1991). B) Researcher calibrating the gravimeter Acknowledgements • Gravity: Drift, Bouger along a line of survey. Special thanks to the Summer Research Program, my advisors Ken Clark and Mike Valentine, and my fieldhands: Ava Feirer-Garrison, Glynis Bawden, Cameron Faccenda, and Akilah Blakey