USING GROUND-FAILURE FEATURES FOR PALEOSEISMIC ANALYSIS Stephen F. Obermeier and Randall W. Jibson, editors USING UQUEFACTION-INDUCED FEATURES FOR PALEOSEISMIC ANALYSIS Chapter A, by Stephen F. Obermeier USING LANDSLIDES FOR PALEOSEISMIC ANALYSIS Chapter B, by Randall W. Jibson U.S. Geological Survey Open-File Report 94-663 This report has not been reviewed for conformity with U. S. Geological Survey editorial standards. Use of brand names in this report is for the sake of description. ACKNOWLEDGMENT Funding for much of the research required for this report was provided by the Earthquake Hazards and Landslide Hazards Programs of the U. S. Geological Survey, as well as by grants from the U. S. Nuclear Regulatory Commission. The Charter A manuscript recieved constructive reviews from John Sims, Alan Nelson, Tom Holzer, Randall Jibson, and Eugene Schweig of the U. S. Geological Survey, from T. Leslie Youd of Brigham Young University, and from Martitia Tuttle of the University of Maryland. Chapter B recieved helpful reviews from Robert Schuster of the U. S. Geological Survey, and from Jim McCalpin of GEO-HAZ, Inc. PREFACE Faults are not exposed at the ground surface or are unavailable for study in many tectonic environments. Therefore other types of geologic evidence are required to reconstruct the prehistoric seismic record of an area. Seismic shaking can produce many different types of ground deformation that can be preserved in the geologic record. Many of the types are discussed in the two papers following, but the papers focus primarily on (1) seismically induced liquefaction features and (2) landslides that move as coherent blocks (slumps and block slides) during seismic shaking. Analysis of both liquefaction-induced features and coherent landslides permits quantitative estimation of levels of prehistoric shaking in many field situations. Most other types of deformations permit only crude estimates of shaking levels. Liquefaction-induced features such as sand-filled fissures are also important because they form only in fairly high levels of seismic shaking: the minimum moment magnitude is about 5.5- 6.0 in most geologic environments. Presence of the sand-filled fissures indicates earthquakes that would have damaged built structures. For landslides, the minimum magnitude is somewhat smaller, about 4.5-5.0 for many types of landslides. Proving a seismic origin for liquefaction-induced features is not very difficult in many geologic environments, particularly where past seismic shaking has been very strong. Independent lines of evidence generally are not required for a definitive assessment of origin. Demonstrating a seismic origin generally involves excluding only a few possible alternate sources for fluidizing sediments, and criteria for doing so have been developed that can be applied to many field situations. Determining a seismic origin for landslides is much more difficult because of the broader range of conditions that can lead to slope failure. Thus, for landslides, multiple, independent lines of evidence of seismic origin generally are required. Paleoseismic ground-failure studies differ fundamentally from paleoseismic fault studies. Whereas fault studies seek to characterize the movement history of a specific fault, ground-failure studies characterize the shaking history of a site or region irrespective of the earthquake source. In regions that contain multiple seismic sources and in regions where faults cannot be studied in detail, which are the norm, paleoseismic ground-failure studies can be particularly valuable tools in hazard and risk assessments. The approaches discussed in these two papers have evolved largely within the past 10 years. The techniques have already been instrumental in greatly advancing the status of knowledge about prehistoric seismicity in diverse regions and geologic settings. In addition, the techniques permit estimation of prehistoric levels of shaking and earthquake magnitude in some cases, which can make the techniques at least as useful as fault studies for gleaning information about paleoseismicity. Stephen F. Obermeier and Randall W. Jibson, editors CHAPTER A USING LIQUEFACTION-INDUCED FEATURES FOR PALEOSEISMIC ANALYSIS STEPHEN F. OBERMEIER U. S. GEOLOGICAL SURVEY OPEN-FILE REPORT 94-663 CHAPTER A CONTENTS ABSTRACT 1. INTRODUCTION 2. OVERVIEW OF THE FORMATION OF LIQUEFACTION- INDUCED FEATURES 2.1 Process of liquefaction and fluidization 2.2 Factors affecting liquefaction susceptibility and fluidization 2.2.1 grain size 2.2.2 relative density 2.2.3 depth of ground-water table 2.2.4 depth and thickness of strata 2.2.5 site effects and nature of seismic shaking 2.2.6 geologic details of the cap 2.2.7 seismic history 2.2.8 age and mineralogy of sediments 3. CRITERIA FOR AN EARTHQUAKE-INDUCED LIQUEFACTION ORIGIN 4. HISTORIC AND PREHISTORIC LIQUEFACTION-SELECTED STUDIES 4.1 Coastal South Carolina 4.1.1 characterization of craters 4.1.2 prehistoric seismicity 4.2 New Madrid Seismic Zone 4.2.1 characterization of venting and fracturing at the ground surface 4.2.2 characterization of sand blows and dikes in sectional view 4.2.3 characterization of sills in sectional view 4.2.4 paleoliquefaction studies 4.3 Wabash Valley Seismic Zone 4.3.1 characterization of features 4.3.2 ages of dikes 4.3.3 evidence for seismic origin 4.3.4 paleoseismic implications 4.4 Coastal Washington 4.4.1 Columbia River features 4.4.2 strength of prehistoric shaking 4.4.3 ancient marine terrace features 5. FEATURES GENERALLY OF NONSEISMIC OR UNKNOWN ORIGIN 5.1 Terrestrial disturbance features 5.1.1 nonseismic sand boils 5.1.2 streambank landslides 5.1.3 ground disturbance by trees 5.1.4 mima mounds 5.2 Features formed in subaqueous environments 5.2.1 load structures in muds 5.2.2 water-escape features in granular sediments 5.2.3 sheet slumps, warped beds, and recumbent folds 5.2.4 turbidity flow features 5.2.5 paleoseismic examples 5.3 Features formed by weathering 5.4 Features formed in a periglacial environment 5.4.1 involutions 5.4.2 ice-wedge casts 6. ESTIMATION OF STRENGTH OF PALEOEARTHQUAKES 6.1 Association with Modified Mercalli Intensity 6.2 Magnitude bound 6.3 Method of Seed and Idriss 6.4 Overview of estimates of magnitude 6.5 Negative evidence CHAPTER A USING LIQUEFACTION-INDUCED FEATURES FOR PALEOSEKMIC ANALYSIS STEPHEN F. OBERMEIER U. S. Geological Survey 922 National Center Reston, Virginia, 22092 ABSTRACT Liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the Holocene. The relatively high shaking level required for their formation makes them particularly valuable as records of strong paleo-earthquakes. This state-of-the-art summary for interpretation and analysis of liquefaction effects takes into account input from both geologic and geotechnical engineering perspectives. Discussed are an overview of the processes involved in formation of the features, criteria for determining whether sediments have been deformed by seismically induced liquefaction, case studies in various geologic settings, and description of the methods for estimating magnitude of prehistoric earthquakes. Also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin. 1. INTRODUCTION This text focuses on the methodology for determining whether observed sediment deformation had a seismic shaking origin or a nonseismic origin. Emphasis is placed on the process of liquefaction, which is the transformation of a granular material from a solid state into a liquefied state as a consequence of increased pore-water pressures (Youd, 1973). The discussion encompasses various manifestations of liquefaction-induced deformation in fluvial and nearshore-marine deposits, and the application of criteria for establishing an earthquake origin. The systematic study of paleoliquefaction is a young discipline. Accordingly, some of the physical parameters that control effects of liquefaction in the field are not completely understood. Still, the principles and methodology for conducting paleoliquefaction studies are sufficiently advanced to warrant their routine application in paleoseismic studies. The method in this text for conducting paleoliquefaction studies was developed largely out of necessity in the United States, where the historic seismic record is particularly short. Paleoliquefaction studies are useful to engineers and planners because of the high shaking threshold required to develop liquefaction features. The threshold is a horizontal acceleration on the order of 0.1 g for strong earthquakes, even in highly susceptible sediment (National Research Council, 1985, p. 34; Ishihara, 1985, p. 352). Worldwide data on historical earthquakes show that features having a liquefaction origin can be developed at earthquake magnitudes as low as about 5, but that a magnitude of about 5.5 to 6 is the lower limit at which liquefaction effects become relatively common (Ambraseys, 1988). (Earthquake magnitude, M, is used rather loosely as either moment magnitude or surface- wave magnitude, whichever is larger.) Liquefaction has been severe and widespread in many worldwide earthquakes. Effects of liquefaction have many manifestations. Some noteworthy reports discuss the effects in the region of the 1811-12 New Madrid, Missouri, earthquakes (Fuller, 1912), in the region of the 1886 Charleston, South Carolina, earthquake (Dutton, 1889), in northern California (Youd and Hoose, 1978), in the vicinity of the 1964 Alaska earthquake