Liquefaction at Finley Quarry, WA?

Two reports by two different teams of geologists describe the same outcrop, sediments, and structural features at Finley Quarry, WA (Coppersmith et al., 2014; Sherrod et al., 2016). Mostly, the teams agreed on what they saw. Where they differed is on liquefaction.

I have visited Finley Quarry several times over the years prior to and since those teams' visits. Several earlier reports are helpful and available online (Jones and Deacon, 1966; Jahns, 1967; Brown, 1968; Bingham et al., 1970; Rockwell, 1979; Farooqui, 1977; Farooqui and Thoms, 1980; Foundation Sciences, 1980). If you need a copy, email me.

Publication of the Sherrod/USGS article surprised me. My spidey sense was raised by some of their unit descriptions and certainly some of their interpretations. After I'd finished reading, I consulted my own field notes and photographs. I found a few apparent discrepancies and emailed a short set of questions to the lead author, a civil service employee with an office at the University of Washington. Receiving no response from him, I contacted his emeritus predecessor at USGS to ask if he might forward my questions. He did, but again, no response. My reply to the Sherrod et al. (2016) article is below.

Mention of a "clastic dike" was first to catch my attention. There are several conspicuous breccia-filled tensile fractures in the high wall of the basalt quarry and I'm familiar with dentical rubble-filled fractures in other basalt quarries in the area (see examples below). I intitially thought that the Sherrod team might have mistaken the rubble-filled fractures for clastic dikes, but not the case. They "dike" they found was clearly enclosed by sediment and labeled a "liquefaction" feature attributed to seismic shaking generated by the Wallula Fault Zone (local portion of the Olympic-Wallowa Lineament). Last movement on Finley Quarry faults was approximated by dating calcium carbonate-cemented fault gouge: middle Pleistocene (U-series method reported in Paces, 2014):

Carbonate‐rich gouge present along the fault exposed at Finley quarry shows complex layering and cementation paralleling the attitude of the fault...ages range from 700 +270/‐160 ka to 224 ±36 ka...These ages are consistent with repeated faulting over a several hundred thousand year time frame in the middle Pleistocene. If younger fracturing and cementation events are present (for instance, the event that formed the colluvial fault wedge dated at 17 ka), they were not sampled in this block of gouge.

Oblique aerial photo of Finley Quarry from Google Earth. View to the east.

My field sketch of the basic geology at Finley Quarry. The area of concern lies at the far left.

Rubble-filled tensile cracks in basalt at Finley Quarry (left side of sketch). There is no vertical offset (shear) associated with the rubble-filled fractures.

Tensile fracture filled with broken basalt fragments exposed in a Grant Count quarry at Frenchman Hills. Identical features are found at Finley Quarry.

Several wide, vertical fractures filled with sediment and fragmented basalt are exposed in a county quarry on the south flank of Rattlesnake Hills. Identical features are found at Finley Quarry.

I believe Sherrod et al. (2016) has misinterpreted an irregular, subhorizontal body of sediment as a liquefaction feature. Neither their photo, nor their interpretive sketch is convincing. The feature does not resemble tabular or tubular clastic dikes known to have been produced by liqufaction. It does not appear to be a sand blow (feeder dike or vented sand/volcanic edifice) nor a sediment-filled ground fissure (lateral spreading). Liquefaction typically requires liquefiable sediment near the water table overlain by a low-permeability cap. Finley Quarry fails all three criteria. Similar features have not been identified in nearby outcrops or reported in the literature over the past century.

I reinterpret their "liquefaction dike/sill (E4)" to be sediment older than Holocene (Units, 17, 18 in Fig. 7.15). It does not appear to cross-cut the modern soil (Holocene "Humic-stained L1 loess"), but appears truncated by it. No source bed is identified and no internal structures (flow, banding, aligned particles) or taper direction is indicated. The feature could just as easily be colluvial material derived from the steep slope adjacent to the pit or a mass of backhoe-disrupted sediment at the highly-disturbed pit located in a steep gully.

Evidence of Holocene liquefaction is not common in Eastern Washington despite abundant wet, unconsolidated alluvium in close proximity to active faults. If the feature at Finley Quarry was produced by liquefaction, similar features should be found nearly everywhere in the region.

The Sherrod team was overenthusiastic in attributing a single ambiguous feature to earthquake-caused liquefaction. Other of their paleoseismic trenching reports show similarly exuberant interpretations. Alternatives should have been more fully considered and discussed in the article. Liquefaction in Eastern Washington should be clearly and unambiguously demonstrated by geologists, given its importance to regional growth plans and seismic hazard assessments.

Figure 7.15 in Coppersmith et al. (2014) shows the outcrop at Finley Quarry examined by the Sherrod/USGS team and the Coppersmith/Quaternary Studies Team. The "liquefaction" feature is circled in red. It does not resemble either part of a sand blow (feeder dike or volcanic edifice) nor does it appear to be a sediment-filled ground fissure (lateral spreading). Colluvium comes to mind. The sketch implies the feature crosscuts Holocene loess, a suspicious relationship.

Geologists from Foundation Sciences, Inc. (Foundation Sciences, 1980, Figure 4) drew this sketch of the Finley Quarry exposure 36 years prior to the Sherrod/USGS study. Considerable surficial material has been removed from the quarry since. Their caption reads, "Sketch of Finley Quarry Fault. Note unfaulted post-flood colluvium and loess overlying older faulted materials.".

Others would seem to agree. Curious comments that appear in a table near the end of the Coppersmith article (Coppersmith et al., 2014, Table 7.2) suggest there were disagreements about field interpretations at Finley Quarry, particularly the feature in question,

The postulated liquefaction feature (dike and sill d) that appears to post-date the deposition of [~11,000 year old Glacier Peak G] tephra is the strongest evidence for a strong shaking earthquake in the general vicinity of Finley quarry (which may or may not be on the RAW-Rattles fault source). The best expressed part of the mapped feature cross cuts Unit 13. The USGS log interprets Unit 13 as L1 loess. However, this unit shares characteristics similar to massive to poorly bedded slackwater deposits observed elsewhere (e.g., at the MCBONEs locality) (i.e., it contains scattered clasts and irregular blocks of pre-flood ice-rafted or ripped up material). Although the mapped extent of the feature up into the modern soil suggests a post-flooding event, additional work or review is needed to preclude a flood-related liquefaction phenomenon.

Liquefaction is a key element in the young, strong seismicity narrative championed by Sherrod's team. Their evidence, however, is at best ambiguous. Their field descriptions are abbreviated and field sketches crucial to their arguments are often crude. Their write up gives the impression that the folks from Seattle are casual visitors bent on making important new discoveries on the East Side, but struggling to comprehend basic aspects of the local geology.

The Finley Quarry site is a highly disturbed exposure and a far cry from anything resembling a type section for surficial units, much less a classic liquefaction locality.

A bit more context may have improved their argument. For example, huge roadcuts that beautifully expose the same strata are located 5 minutes west of Finley Quarry. Roadcuts along Hwy 397 extend for a few hundred meters and are twenty meters high. All are hikeable. Large pullouts that accommodate several vehicles exist. Dozens of sheeted Pleistocene-age clastic dikes there cut sediments and bedrock. None are liquefaction features.

To date, no clastic dikes of Pleistocene age in Eastern Washington have been shown to ascend from a buried (liquefied) source bed. Likewise, I am unaware of any reports describing Holocene liquefaction dikes east of the Cascades. Perhaps recent trenching by USGS has uncovered liquefaction evidence near Yakima Fold Belt faults (i.e., Bennett's work), but that work has yet to be published. Liquefaction at Finley Quarry is not significant.

Large, excellent exposures easily accessed from the road are found along Hwy 397 a short drive west from Finley Quarry. If you examine Finley Quarry, you should come here too in order to resolve stratigraphic and structural relationships. Any liquefaction evidence here?

Drive by geology. Hasty sketch of strata exposed in Hwy 397 roadcut shown in photo above. Many details left out.

Reese Coulee roadcut along Hwy 12 between Lowden and Wallula seems to show sediments similar to those exposed along Hwy 397.

Refs

Bingham et al., 1970, Geologic investigation of faulting in the Hanford region, Washington with a section on the occurrence of microearthquakes, U.S. Atomic Energy Commission, Division of Reactor Development and Technology Report #90-27, 126 pgs.

Camp et al., 2017, Field-Trip Guide to the vents, dikes, stratigraphy, and structure of the Columbia River Basalt Group, eastern Oregon and southeastern Washington, USGS/DOI Scientific Investigations Report 2017–5022–N, p. 65-66

Cooley, S.W., 2020, Sheeted clastic dikes in the megaflood region, MT-WA-OR-ID, Northwest Geology (Tobacco Root Geological Society), v. 49

Coppersmith et al., 2014, Appendix E: Structural analysis and Quaternary investigations in support of the Hanford PSHA in Hanford Sitewide Probabilistic Seismic Hazard Analysis, Pacific Northwest National Lab Report #23361

Foundation Sciences, Inc., 1980, Geologic reconnaissance of parts of the Walla Walla and Pullman, Washington, and Pendleton, Oregon 1 degree x 2 degree AMS quadrangles, a consultant's report to U.S. Army Corps of Engineers-Seattle District, Contract DACW67-80-C-0125, 144 pgs.

Jenkins, O.P., 1925, Clastic dikes of eastern Washington and their geologic significance, American Journal of Science, 5th Series, v. 10

Paces, J.B., 2014, 230Th/U ages supporting Hanford site-wide Probabilistic Seismic Hazard Analysis, AMEC/PNNL/USDOE Office of Environmental Management/USGS Report, 28 pgs.

Sherrod et al., 2016, Active Faulting on the Wallula Fault within the Olympic-Wallowa Lineament, Washington State, USA, Geological Society of America Bulletin v. 128