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In the U.S. Pacific Northwest (PNW), the historic earthquake record is often insufficient to provide inputs to seismic-hazard analyses or to inform ground-motion predictions for certain seismic sources (e.g., the Cascadia Subduction Zone, CSZ). As a result, paleoseismic studies are commonly used to infer information about the seismic hazard. However, among the many forms of coseismic evidence, soil liquefaction provides the best, if not only, evidence from which the intensities of previous ground motions may be constrained. Accordingly, the overarching goal of this research is to use paleoliquefaction to elucidate previous ground motions in the PNW – both for CSZ events and others – and to further constrain the locations, magnitudes, and recurrence rates of such ruptures. Towards that goal, this paper: (i) reviews current paleoliquefaction inverse-analysis methods and their limited, prior applications in the PNW; (ii) compiles all PNW paleoliquefaction evidence from the literature into a GIS database, resulting in data from 185 study sites (e.g., feature locations, types, sizes, and ages); and (iii) develops maps – specific to the CSZ – that forecast paleoliquefaction for 30 different simulations of a CSZ event. These maps can be used to guide field explorations for new evidence, such that they are conducted efficiently and strategically, considering the apparent utility of evidence toward constraint of CSZ ground-motion models. Of additional utility, this process provides regional ground-motion predictions for physics-based simulations of an M9 event, to include expected site effects. Collectively, the maps of expected shaking intensity and liquefaction may be useful in downstream hazard modelling, regional loss estimation, policy development, and science communication. Ultimately, as more paleoliquefaction evidence is identified and studied, better constraint of regional ground-motion hazards will result. Version 2 (this posting) supersedes Version 1 (10.17603/ds2-jm19-2w09). Updates include GIS rasters that provide regional ground-motion intensity predictions (PGA, PGV) for 30 physics-based simulations of an M9 event, to include expected site effects
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The Stratigraphy of Compound Sand Blows at Sites of Recurrent Liquefaction: Implications for Paleoseismicity Studies
Paleoliquefaction studies provide valuable information for seismic hazard analyses in areas where the return period of moderate to large events is longer than the duration of the historical earthquake catalog (e.g., Central-Eastern and Pacific Northwest United States). Toward this end, paleoliquefaction studies require accurate and detailed assessments of individual features and of the extent of the paleoliquefaction field for the event, with the difficulty of accurately interpreting field observations increasing in areas where recurrent liquefaction was triggered by spatiotemporally clustered paleo events. Accordingly, undisturbed features formed by recurrent liquefaction during the 2010–2011 Canterbury, New Zealand, earthquake sequence were studied to facilitate interpretation of paleoliquefaction analogs. Silt drapes demarcated multiple episodes of liquefaction in the sand blows, with the thickness of the silt drapes correlating to the fines content of the liquefied source stratum. However, no ubiquitous trends in the spatial sorting of grain sizes in the coarser fraction of the ejecta underlying silt drapes were observed. This study provides a modern analog to recurrent paleoliquefaction evidence and has important implications for interpretation of seismic hazards.
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- PAR ID:
- 10134678
- Date Published:
- Journal Name:
- Earthquake Spectra
- Volume:
- 35
- Issue:
- 3
- ISSN:
- 8755-2930
- Page Range / eLocation ID:
- 1421 to 1440
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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In regions of infrequent moderate-to-large earthquakes, historic earthquake catalogs are often insufficient to provide inputs to seismic-hazard analyses (i.e. fault locations and magnitude–frequency relations) or to inform ground-motion predictions for certain seismic sources. In these regions, analysis of relic coseismic evidence, such as paleoliquefaction, is commonly used to infer information about the seismic hazard. However, while paleoliquefaction studies have been performed widely, all existing analysis techniques require a priori assumptions about the causative earthquake’s location (i.e. rupture magnitude and ground motions can otherwise not be estimated). This may lead to inaccurate assumptions in some settings, and by corollary, erroneous results. Accordingly, this article proposes an inversion framework to probabilistically constrain seismic-source parameters from paleoliquefaction. Analyzing evidence at regional scale leads to (a) a geospatial likelihood surface that constrains the rupture location and (b) a probability distribution of the rupture magnitude, wherein source-location uncertainty is explicitly considered. Simulated paleoliquefaction studies are performed on earthquakes with known parameters. These examples demonstrate the framework’s potential, even in cases of limited field evidence, as well as important caveats and lessons for forward use. The proposed framework has the potential to provide new insights in enigmatic seismic zones worldwide.more » « less
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Given the likelihood of future M9 Cascadia Subduction Zone (CSZ) earthquakes, various estimates of the resulting, regional ground motions have been made, including a suite of 30 physics-based simulations that reflect key modeling uncertainties. However, because the last CSZ interface rupture occurred in 1700 CE, the shaking expected in such an event is especially uncertain, as are the impacts to the built and living environments. Like other coseismic impacts, soil liquefaction poses a significant threat and must be considered by any scenario study used to inform planning and response, or to focus mitigation resources. Liquefaction is also notable for its potential to “ground truth” ground-motion estimates, given that its presence or absence in the geologic record can provide constraint on the intensities of shaking in past events. It is thus an important phenomenon looking both forward and backward. Accordingly, using recent physics-based simulations, this study (1) predicts liquefaction in M9 CSZ ruptures at 400 locations in Oregon, Washington, and British Columbia (BC) using an array of cone-penetration-test based models and (2) uses paleoliquefaction evidence at ten sites spanning from Southern Oregon to Vancouver, BC to constrain possible ground-motion intensities experienced in the 1700 CE earthquake. The forward predictions indicate that liquefaction in M9 events could be pervasive in the region and affect numerous population hubs, with the potential for damage across hundreds of square kilometers. The backward analyses suggest that 1700 CE ground-motion intensities may have been less than expected from M9 simulations in some northern portions of the CSZ (e.g. Seattle), given the paucity of 1700 CE liquefaction evidence in these areas. Ultimately, further discovery and analysis of CSZ paleoliquefaction, or lack thereof, will confirm or modify this possibility and the conclusions drawn herein.more » « less
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This dataset comprises a subsurface characterization of key liquefaction areas in İskenderun, Türkiye, following the February 6, 2023, Kahramanmaraş earthquake sequence. Field testing was conducted from March 18 to March 27, 2024. The dataset includes Cone Penetration Tests (CPT) as well as seismic CPTs (SCPT) and incorporates pore pressure dissipation measurements, shear wave velocities, and standard CPT readings. High-quality subsurface investigations, such as this dataset, are a key component of liquefaction case histories. As such, this data is vital for future analyses of liquefaction-induced building settlements, building-ground interactions, and liquefaction-induced ground deformations resulting from the Kahramanmaraş earthquake sequence.more » « less
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Physics-based ground motion simulations are a valuable tool for studying seismic sources with missing historical records, such as Cascadia Subduction Zone (CSZ) interface earthquakes. The last such event occurred in 1700 CE and is believed to be an M8-M9 rupture. The United States Geological Survey recently developed 30 physics-based simulations of a CSZ rupture to predict ground motions across the Pacific Northwest. Consideration of key modeling uncertainties across these simulations leads to estimates of ground motion intensity that vary by ~100% in some areas (e.g., Seattle). Paleoliquefaction, or soil liquefaction from past earthquakes, provides the best geologic evidence for constraining or "ground truthing" the intensity of past shaking, yet while paleoliquefaction has been documented throughout Cascadia, limited analyses have been performed to exploit this evidence. This study focuses on Kellogg Island, 2 mi south of Seattle, where liquefaction has been documented from several earthquakes, but not from the 1700 CE event. Therefore, using the CSZ simulations and in situ cone penetration test data, this study predicts the probability of surficial liquefaction manifestation at Kellogg Island during an M9 CSZ event. As part of this effort, velocity profiles are developed from multichannel analysis of surface waves, and non-linear site response analyses are used to propagate simulated motions to the surface. Results show a high probability of liquefaction near Kellogg Island for most simulations, whereas to date no evidence of 1700 CE liquefaction has been discovered at Kellogg Island, nor at any other location in the Puget Sound. The discrepancy between predictions and observations might indicate that the 1700 CE ground motions were less intense in Seattle than most predictions of M9 earthquakes indicate. Toward the goal of elucidating the expected impacts of future CSZ earthquakes, similar analyses are ongoing at additional sites across the region.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1193/041818EQS097M
