Ray E. Wells, U.S. Geological Survey

Block Rotations and Earthquake Hazards in the Pacific Northwest

  • DINNER MEETING - Tuesday, June 6, 2006
  • Location: Stanford University

  • 5:30 PM-Social (3/4) Hour: . . . Mitchell Bldg., first floor (Hartley)
  • 6:15 PM-Dinner: . . . Mitchell Bldg., first floor (Hartley)
  • 7:30 PM-Meeting: . . . GeoCorner Room 320-105

    see Map showing Mitchell and GeoCorner Room 320

    Anyone wishing to attend the lecture only is welcome at no cost.

    This will be the 381st meeting since 1954

    thumbnail view of map of Cascades from northern California nearly to Canada


    In 1957 Allan Cox reported in Nature that the paleomagnetic pole for the Eocene Siletz River Volcanics (SRV) of the Oregon Coast Range lay far to the east of the geocentric axial dipole, an oddity that defied adequate explanation for nearly two decades. Subsequent studies have shown that the Oregon Coast Range (OCR) has rotated clockwise more than 70° since 50 Ma, and that rotation decreases northward into Canada, southward into California, and eastward into the backarc. The rotations are thought to be driven by Basin and Range extension and dextral shear between N. America (NA) and northward-moving oceanic plates to the west. The block rotations are related to patterns of seismicity and volcanism in Cascadia, and GPS data from McCaffrey and others indicates rotations are still occurring. We have created independent block models that honor the paleomagnetic and GPS data, and they are very similar. We can combine the paleomagnetic, geologic, and GPS data into a single model of plate-like blocks bounded by elastic fault zones The rotation pole for the OCR lies nearby in northeastern Oregon. Calculated forearc velocities are consistent with the rate and direction of extension in the Basin and Range province, the change from extension in the southern Cascade arc to compression in the northern arc, and the northward shortening and crustal seismicity in western Washington as it is compressed against the Canadian Coast Mountains buttress. The rate of shortening across western Washington and the Puget Lowland is 4.4±0.3 mm/yr, sufficient to drive the Seattle fault and many other recently discovered active faults in the Lowland.

    About the Speaker

    Photo of Ray

    Ray's specialties include geologic mapping, Pacific Northwest geology and tectonics, geology of the Cascadia forearc, crustal deformation and neotectonics of convergent margins, structure of subduction zones, paleomagnetism . Ray's current work includes

    Reservations: The preferred way to make reservations is simply to email Janice Sellers at by June 2, tell her you will attend, commit to pay, and bring your payment to the meeting. Janice always emails a confirmation; if you don't get one, assume email crashed yet again and email her a second time. A check made to "PGS" is preferred, payable at the meeting.

    If you want to pay in advance:

    Stanford faculty and students: Please make dinner reservations by June 2. Contact Dr. Elizabeth Miller via her mailbox (and leave check), Geological and Environmental Sciences Office, Geocorner - Bldg. 320 (Rm. 205). Make checks out to "PGS."

    All others, including faculty and students from other Bay Area universities and colleges and USGS: Please make dinner reservations by June 2. Contact Janice Sellers, at 1066 28th Street, Oakland, CA 94608-4547, (510) 268-8254 . Send check made out to "PGS" to Janice.

    Dinner is $30.00. Includes wine (5:30 to 6:15 PM.) and dinner (6:15-7:30 PM.).

    For students from all universities and colleges, the dinner, including the social 3/4-hour, is $5.00 and is partially subsidized thanks to the School of Earth Sciences, Stanford University (Note, no-show reservations owe the full price).

    Doris and George will be in Hawaii but Elizabeth has grand plans for a good feast so come along and see <backspace> taste for yourself.

    Dues for Academic Year 2005-2006 ($10.00) should be sent to Janice Sellers, 1066 28th Street, Oakland, CA 94608-4547. Janice's phone: (510) 268-8254.

    Officers: Ray Wells, President; Dwight Harbaugh and Elizabeth Miller, Co-Vice Presidents; Mike Diggles, Secretary; Janice Sellers, Treasurer; Bob Coleman, Field-Trip Czar

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    Date created: May 30, 2006
    Last modified: May 30, 2006
    Created by: Mike Diggles, Webmaster-Secretary, PGS.

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