High-Resolution Seismic Reflection Imaging of Growth Folding and Shallow Faults beneath the Southern Puget Lowland, Washington State

Abstract

Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ∼350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ∼2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ∼3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

Diverse rupture modes for surface-deforming upper plate earthquakes in the southern Puget Lowland of Washington State

“…Shallow seismic refl ection work has confi rmed the growth fold and other folds to the west, and identifi ed small faults near the northwest-trending monocline that indicate its postglacial growth. Clement et al (2010) interpreted the refl ection data to suggest Holocene folding and faulting along the Olympia fault (or fold) on the south edge of the Tacoma basin. If north-dipping reverse faults of the Tacoma fault zone sole into a south-dipping master Seattle thrust, they do so at a depth of at least 10 km (Fig.…”

“…These linear, 1-6-m-high scarps extend 4.4 km east-west between Hood Canal and Case Inlet (Sherrod et al, , 2004bLogan and Walsh, 2007;Nelson et al, 2008, sheet 1) and probably another 2 km to the east beneath Case Inlet (Figs. 1C and 2B;Johnson et al, 2004b;Clement et al, 2010). Seismic refl ection profi ling east of Allyn shows that the water bottom of Case Inlet on trend with the scarp is warped upward ~2 m, suggesting Holocene growth of a fold above a blind thrust (Johnson et al, 2004b;Clement et al, 2010).…”

“…If north-dipping reverse faults of the Tacoma fault zone sole into a south-dipping master Seattle thrust, they do so at a depth of at least 10 km (Fig. 3B;Brocher et al, 2001Brocher et al, , 2004Johnson et al, 2004b;Clement et al, 2010).…”

Determining the Basaltic Sequence Using Seismic Reflection and Resistivity Methods

“…Philip et al (2004) applied it to image a thin, diamondiferous kimberlite dyke. Clement et al (2010) used it to delineate growth folding and shallow faults beneath the southern Puget lowland inWashington state.…”

Seismic and geoelectric study of the basaltic sequence in the south of Al-Madinah

“…For instance, Philip et al (2004) applied it to image a thin, diamondiferous kimberlite dyke. Clement et al (2010) used it to delineate growth folding and shallow faults beneath the southern Puget lowland in Washington state. Cocker et al (1997) used it to assist in mine planning and future horizontal drilling for coal-seam methane extraction.…”