The Doty : What is its place in modern crustal deformation of southwest ? Megan Anderson ([email protected]), Todd Lau, Wesley von Dassow, Tabor Reedy, Andrew Sadowski, Alison Horst, Alec Lockett, 5 Kinematic Relationships T33D-0404 If the Doty fault zone (DF) and nearby faults accommodate most of the relative motion Rebeca Becerra, Conner Toth, Cat Samson, Alex Steely, Michael Polenz between the TACO and PORT blocks of McCaffrey and others (2013; two arrows below), Washington Geological Survey, Olympia, WA we expect major reverse and minor left-lateral displacement on the DF, major right-lateral and minor reverse displacement on the Fall River fault (FRF), and significant reverse displacement on the Scammon Creek (SCF) and Kopiah faults (KF), which broadly fits our interpretation below. Box shows location of lidar in Section 4. All faults here are shown simplified in red on the map below with additions from 2019 data collection. Tectonic Setting 1 Geological Mapping Detailed geologic mapping 4 Recent Fault Activity? (inside black outline) confirms Block rotation model for the Pacific Northwest from general geometries and contact Wells and others (1998). Rotational motions are -123°22.5’ -123°15’ Lidar image along Doty fault zone segment (see boxes left and right for constrained by very long baseline interferometry, relationships defined by Pease location). Unlike the Puget Lowland around , clear fault scarps are paleoseismology, magmatic arc spreading, and and Hoover (1957). The Doty not apparent in the Doty fault region. Though this may indicate these faults Pacific–North America motions. The western Oregon fault does not appear to continue have been inactive in the Quaternary, any scarps that form could have low block (pink) rotates about the OC-NA pole. A weaker west of its previously mapped preservation potential due to lack of compact near-surface substrate western Washington block (green) accommodates D’ extent, and bedding attitudes 46°45’ combined with a low displacement rate. Near-surface materials are instead north–south shortening between Siletzia and the seem to indicate a structure highly weathered, loose regolith in most places. There are few locations slower-moving Canadian Coast Mountains. The limits of stepping north and west. New with preserved Quaternary deposits at all. One location with preserved Q is the deforming western Washington block are not well interpretations increase the along the Chehalis River, crossing model profile C–C’ (circle below) and the known. The Doty fault is one of several east-trending geologic cross-section line length and significance of the Rainbow Falls Doty fault strand. This strand also has the clearest compressional structures in western Washington that Martin Creek fault. Magenta box could currently be accommodating N–S compression. associated lidar lineament. shows the location of the lidar image, right, in Section 4.

geophysical model line Major Geologic Units

Qa Quaternary alluvium D Linear river Qls segment Quaternary landslide Rainbow Falls strand Lineaments location from C-C’ C „vb Miocene Columbia River The Doty fault zone extendseast far GPS data constrain more precise models of ER Line present-day crustal movement (McCaffrey and enough (with a couple of steps) to meet „cs Miocene continental others, 2016). GPS velocities show the effect of both sandstone the St. Helens Seismic zone, which crustal rotation around a pole in eastern could form the NE edge of McCaffrey’s WA–northern ID and elastic deformation due to „ms Miocene marine sandstone PORT block. Brocher and others’ (2017) locking along the subduction interface. rotational schema predicts …Em Oligocene-Miocene Lincoln lc ER image along lidar lineament shown above. S N Creek Formation (sedimentary) predominantly reverse displacement on Removing Resistive Columbia River Basalt (CRB) is exposed the DF and Rochester fault (RF) and a transient combination of reverse and right-lateral En Skookumchuck at the surface and seems to be duplicated below, elastic sk strike-slip displacement on the SCF and Formation (sedimentary) matching the gravity/magnetics model (shown See below, Section 3, for KF. The FRF should be right-lateral deformation 46°37.5’ here in the opposite orientation for comparison). model segment location. highlights Em Eocene McIntosh Formation strike-slip, which does not match our crustal (sedimentary) S N interpretation. This may indicate that rotation and CRB crustal blocks are not moving in a pure Eocene Crescent Formation supports Evc CRB? rotational frame, perhaps (basalt) modeling the accommodating some permanent independent deformation from compression along the movement of subduction zone. There may also be an crustal blocks. early deformational history that is not This block captured by the present kinematic field. model by McCaffrey and others Broadly, faults and seismic lineaments (yellow) (Transect A not shown on paralleling concentric circles around a rotational pole in Subsurface Fault Geometry Modeling (2013) places this poster.) 2 Fault Extent 3 eastern WA show right-lateral transform displacement. Location shown left, Section 2 the southern D Location shown left and above, Sections 1 and 2 D’ A A’ Faults subperpendicular to the rotation direction (gray) More than 2000 new 500 edge of the “Taco” block, which is locked, 1000 show predominantly compressional offset (Brocher and gravity measurements Conclusions & Continuing Work roughly along the Doty fault. This block 750 others, 2017). The location of our study area in in the last 3 years have 250 boundary accommodates < 1 mm/yr RF OS 500 southwest WA (black box) is a zone of missing data. made gravity a key tool The ‘50s-era mapping was correct! Our work confirms unusual shortening and 1–2 mm/yr left-lateral B’ 250 Magnetics (nT) Magnetics (nT) 0 1 slip. for identifying faults =Observed =Calculated (?) right-angle intersections for faults and folds in the region. SCF A’ 0 D’ through lineament MCF 50 KF =Observed =Calculated B 30 D analysis and modeling 40 The western end of the Doty fault connects to a NW-stepping FRF C (right). Completed work 30 20 DF Bend DF 2 set of faults. The east end appears to step slightly south to confirms a minimum 20 10 Gravity (mGal) DF length of 41 km for the Gravity (mGal) 10 connect to the St. Helens seismic zone. A 0 Doty fault and data WA State #1 Major Research Questions ? S BHV029 Seifert #1 N DF

flight path SZF C’ W E SCF KF collection in the summer flight path 0 The Doty fault and many others in the area are zones of closely FRF of 2019 extends its ? Was the ‘50s-era 0 3 spaced fault strands, some likely blind. All have some associated gradient to 5000 component of reverse and transform displacement. Depth (ft) Depth (ft) geologic mapping 69 km total (roughly the 5000 1 ? 10000 correct? SHSZ same length as the ? ? ??? Recent activity is unclear. Further geophysical imaging DF: Doty fault zone Seattle fault), nearly 0 15000 30000 45000 0 15000 30000 45000 60000 Units adjacent to and deformed by the Doty FRF: Fall River fault VE =1 meeting the St. Helens Distance (ft) VE =1 Distance (ft) fault were mapped with a 90° change in KF: Kopiah fault 4 (planned, April 2020), including ER, active seismic, and GPR MCF: Martin Creek fault seismic zone (SHSZ). C Location shown left and above, Sections 1 and 2 C’ B Location shown left, Section 2 B’ strike, which is unusual. OS: Olympia structure 500 500 may resolve this. SCF: Scammon Creek fault 250 Pease and Hoover (1957) geologic map SHSZ: Mt. St. Helens The crust of southwestern 250 seismic zone 0 Slip Rates (mm/yr) Relative displacement on the faults studied is broadly

with roughly the same bounds as that shown RF: Rochester fault Magnetics (nT) Washington is composed Magnetics (nT) Post CRB (16.4 Ma) in Section 1, above right. -250 =Observed =Calculated consistent with two proposed regional frameworks for RF OS predominantly of Doty fault zone 0.05 5 =Observed =Calculated deformation. The Fall River fault displacement doesn’t entirely B’ of the Crescent 50 Fall River fault 0.08 40 fit and indicates that our understanding is incomplete. SCF A’ Formation, the local 40 30 Post Crescent (50.5 Ma) Is the Doty fault really MCF D’ Siletzia member unit.

KF Gravity (mGal) How does the Doty B 20 Doty fault zone 0.05 3 a zone? D FRF Eocene to Miocene Gravity (mGal) 30 C Fall River fault 0.09 DF onshore and coastal 2 fault connect to the DF SW NE Scammon Creek KF Previous research suggested the Doty is a flight path SCF fault zone 0.05 sedimentary partly strata Nflight path S 0 regional fault network? reverse fault. This work will test this DF blanket the basalt. Fault DF Salzer Creek fault 0.01 Acknowledgments hypothesis to confirm its kinematic A 0 Prior mapping did not show the Doty fault ? offsets juxtaposing these 5000 Depth (ft) Thanks to special project Capitol Budget funding from the State of Washington for the Chehalis relationship to crustal deformation. This C’ Depth (ft) ? endpoints connecting to any other faults. two lithologies provide an Physical properties Basin Study and to the StateMap Program for additional funding. We appreciate help and advice research will also determine if the fault is 5000 ? excellent target for gravity 45000 60000 75000 0 15000 30000 45000 used in modeling, densities of the U.S. Geological Survey Geophysics Unit at Menlo Park (GUMP), particularly Dan Schierer VE =1 3 really a zone with multiple strands. and geomagnetic VE =1 Distance (ft) Distance (ft) relative to 2670 kg/m . and Tait Earney. Thanks especially to Rick Blakely and Lydia Staisch for their advice, ideas and generous sharing of early data and results. Is the Doty fault active? mapping because of their Modeling of subsurface geometries in cross section constrained by Density SHSZ contrast Susceptibility Remanence 4 3 -3 contrasting density and surface geology, wells, aeromagnetic, ground magnetic, and isostatic (kg/m ) (χ = 10 SI) (A/m) Geologic units What is the Doty fault’s χ = 0 Qa – Alluvium No clear scarps are visible in lidar data for magnetic properties. gravity anomalies confirms fault dip and strongly suggests multiple Δρ= -660 References Δρ= -470 to -660 χ = 0 Qapo – Logan Hill Formationlh Brocher, T. M., Wells, R. E., Lamb, A. P., Weaver, C. S., 2017, Evidence for distributed clockwise rotation of the crust in the northwestern United States from fault Crescent Formation is χ = 0 -1.3 or 0 „cs – Continental sandstone the region. This may indicate the Doty and 5 role in regional crustal strands for several of the faults. Some faults could be blind. Sedimentary Δρ= -660 geometries and focal mechanisms, Tectonics, 36, p. 787-818. other local faults are inactive. However, lack magnetic (~45 SI) and stratigraphy consistently thins over the uplifted blocks suggesting a long Δρ= -70 to 30 χ = 15 to 80 „vb ( sp / gs) – Columbia River Basalts Blakely, R. J., Wells, R. E., Sherrod, B. L., Brocher, T. M., 2016, Segmentation of the Cascadia forearc in southwestern Washington-evidence from new potential-field deformation kinematics? 3 Δρ = -470 χ = 0 „ms – Marine sandstone data: AGU Fall Meeting, 12-16 December, abstract #GP34A-04. of consolidated glacial deposits and a thick dense (~2830 kg/m ) and history of faulting and/or folding since the Eocene. Most faults have Δρ = -70 χ = 80 Evb – Basalt of uncertain affinity Johnson, S.Y., Blakely, R.J., Brocher, T.M., Haller, K.M., Barnett, E.A., Bucknam, R.C., Haeussler, P.J., Pratt, T.L., Nelson, A.R., Sherrod, B.L., Wells, R.E., Lidke, D.J., sedimentary units are Δρ = -400 to -430 χ = 0 to 10 …Em lc – Lincoln Creek Formation Harding, D.J., and Kelsey, H.M., compilers, 2016, Fault number 570, Seattle fault zone, in Quaternary fault and fold database of the United States: U.S. carapace of highly weathered regolith may To understand full hazard potential, defining significant vertical throw (≤ 3.4 km) and steady-slip rates between Eocene Δρ= -370 χ = 0 to 5 En – Skookumchuck Formationsk Geological Survey website, https://earthquakes.usgs.gov/hazards/qfaults. Ev /Ev ? – Northcraft Formation and McCaffrey, R., King, R. W., Payne, S. J., Lancaster, M., 2013, Active tectonics of the northwestern U.S. inferred from GPS-Derived surface velocities, Journal of High-resolution aeromagnetic data (Blakely and others, 2016) largely nonmagnetic (~0 SI) and Δρ= -70 χ = 35 n n lead to poor preservation. Other approaches current driving forces, whether from forearc and Miocene, but at a fraction of the Seattle fault’s rate (~0.9 mm/yr; unknown magnetic rocks Geophysical Research, 118(2), p. 709-723. - χ Em – Upper McIntosh Formation confirm lineament locations identified from gravity and support modeling (right). less dense (~2150 Δρ= -220 to 240 = 0 to 3 1m Pease, M. H. Jr., Hoover, L., 1957, Geology of the Doty-Minot Peak area, Washington: U.S. Geological Survey Oil and Gas Inventory Map OM-188. are needed to clearly answer this question. rotation or subduction, is important. Johnson and others, 2016). Box on C–C’ is shown in Section 4, above. Δρ= -220 to -240 χ = 0 to 3 Em 2m – Lower McIntosh Formation 3 Wells, R. E., Weaver, C. S., Blakely, R. J., 1998, Fore-arc migration in Cascadia and its neotectonic significance, Geology, 26(8), p. 759-762. Both gravity and magnetic datasets confirm the Doty fault does not extend kg/m ). Δρ = 140 to 190 χ = 19 to 70 0.5 or 0 Ev c (R) – Reversely magnetized Crescent Formation west of its geologically mapped extent. Δρ = 140 to 190 χ = 19 to 70 0.5 or 0 Ev c – Normally magnetized Crescent Formation This poster will be archived shortly after AGU at: https://www.dnr.wa.gov/programs-and-services/geology/publications-and-data/presentation-archive