Geologic Folio of the Olympia-Lacey-Tumwater Urban Area, Washington: Liquefaction Susceptibility Map
Total Page：16
File Type：pdf, Size：1020Kb
C) 0. ro ~ C) O> 0 Geologic Folio of the 0 (1) (9 Olympia-Lacey-Tumwater Urban Area, Washington: Liquefaction Susceptibility Map by Stephen P. Palmer, Timothy J. Walsh, and Wendy J. Gerstel WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Geologic Map GM-4 7 January 1999 Partially supported by the Federal Emergency Management Agency and the Washington Division of Emergency Management The information provided In this map cannot be substituted for a site-specific geotechnical investigation, which must be performed by qualified practitioners and is required to assess the potential for and consequent damage from soil liquefaction. Location of area WASHINGTON STATE DEPARTMENT OF Natural Resources Jennifer M. Belcher -Commissioner of Public Lands Geologic Folio of the Olympia-Lacey-Tumwater Urban Area, Washington: Liquefaction Susceptibility Map by Stephen P. Palmer, Timothy J. Walsh, and Wendy J. Gerstel WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Geologic Map GM-47 July 1999 The information provided in this map cannot be substituted for a site-specific geotechnical investigation, which must be performed by qualified practitioners and is required to assess the potential for and consequent damage from soil liquefaction. Jennifer M. Belcher -Commissioner of Public Lands Division of Geology and Earth Resources DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the State of Washington, nor any agency thereof, nor any of their employees, makes any war ranty, express or implied, or assumes any legal liability or re sponsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorse ment, recommendation, or favoring by the United States Gov ernment or the State of Washington or any agency thereof. The views and opinions of authors expressed herein do not neces sarily state or reflect those of the United States Government or the State of Washington or any agency thereof. WASHINGTON STATE DEPARTMENT OF NATURAL RESOURCES Jennifer M. Belcher-Commissioner of Public Lands DIVISION OF GEOLOGY AND EARTH RESOURCES Raymond Lasmanis-State Geologist J. Eric Schuster-Assistant State Geologist This study was partially supported by grants provided by the Washington Division of Emergency Management, Military Department under Agreements No. 4-94-631-001 and No. 4-95-632-001 with funding provided by the Federal Emergency Management Agency. This report is available from: Publications Washington Department of Natural Resources Division of Geology and Earth Resources PO Box 47007 Olympia, WA 98504-7007 Price $2.32 Tax (WA residents only) _.,ll. Total $2.50 Mail orders must be prepaid. Please add $1.00 to each order for postage and handling. Make checks payable to the Department of Natural Resources. Map printed on acid-free paper. Pamphlet and envelope printed on recycled paper. Printed in the United States of America Geologic Folio of the Olympia-Lacey-Tumwater Urban Area, Washington: Liquefaction Susceptibility Map Stephen P. Palmer, Timothy J. Walsh, and Wendy J. Gerstel Washington Division of Geology and Earth Resources PO Box 47007; Olympia, WA 98504-7007 INTRODUCTION have been correlated with geological units mapped at 1:24,000 The Washington Department of Natural Resources, Geology scale (1 in.= 2,000 ft or 1 cm= 240 m). Because of the regional and Earth Resources Division, is actively investigating earth nature of this map, only generalized areas prone to liquefaction quake hazards statewide and has concentrated its technical pro can be delineated, and only a relative susceptibility (ranging gram on mapping deposits in the Puget Sound region that are from very low to high) is assigned to these areas. This map can subject to seismically induced soil liquefaction. The purpose of not be used to determine the presence or absence ofliquefiable this report is to present the technical evaluation used in gener soils beneath any specific locality. Likewise, no estimate of the ating the accompanying liquefaction susceptibility map of the ?amage resulting from liquefaction is presented in this study; Olympia-Lacey-Tumwater urban area. This map encompasses m many instances, liquefaction may occur without causing sig the Olympia-Lacey-Tumwater Urban Growth Area, the allu nificant ground displacement and consequent damage to struc vial valley along the lower reach of the Nisqually River, and tures. the low-lying tidal marsh and alluvial plain in the vicinity of This map cannot be substitutedfor a site-specific geotech Mud Bay. nical investigation, which must be performed by qualified Liquefaction occurs when a water-saturated, sandy soil practitioners and is required to assess the potential for lique loses strength during vibratory shaking, such as that generated faction and consequent damage at a given locality. by an earthquake. Below the ground-water table, the pore space The liquefaction susceptibility map presented in this report between sand grains is filled with water, and the weight of the is based on recent 1:24,000-scale geologic mapping conducted overlying soil mass is ordinarily supported by grain-to-grain in support of this project and the analyses of 23 l geotechnical contact. Strong shaking during a large earthquake can disrupt borings obtained from the Washington State Department of the grain-to-grain contact, causing a decrease in the grain sup Transportation and local government agencies. Four catego port. If strong shaking lasts long enough, the grain structure of ries of geologic deposits found in the study area are assigned a a loose sandy soil may completely collapse. When the grain relative liquefaction hazard ranking determined through analy contact support is lost, the pore-water pressure must increase to sis of the geotechnical data, geological characterization, and account for the stresses imposed by the overlying weight of the historical reports of liquefaction during the 1949 Olympia soil mass. At this point, the sandy soil is liquefied and will tem (magnitude 7 .1) and 1965 Seattle-Tacoma (magnitude 6.5) porarily behave as a viscous fluid, causing an immediate loss of earthquakes. soil strength. The liquefied soil may then be subject to extreme Artificial fill and Holocene (younger than I 0,000 years) al lateral deformation because it does not provide much resis luvium are determined to have a high susceptibility to liquefac tance to horizontal forces. Such lateral spreading of the soils tion. The high liquefaction hazard in portions of downtown within and above the zone of liquefaction can cause tremen Olympia underlain by fill is well quantified based on the analy dous damage to buildings and buried utilities located on the sis of91 borings located in this area. The high liquefaction haz moving soil mass. The collapse of the grain structure can result ard area encompassing the Deschutes River valley is defined in settlement of the soil column and loss of soil bearing capac using measured shear wave velocities obtained in a boring ity, which may cause severe damage to structures. The buoyant drilled in Pioneer Park. Analyses of geotechnical borings forces within a liquefied soil mass can cause flotation of under drilled in the Nisqually River valley and Mud Bay area indicate ground tanks, pilings, and other buried structures. that liquefiable soils are present, but quantitative characteriza The accompanying map is intended to provide building of tion of the hazard in these areas cannot be performed because ficials, land-use planners, emergency-response personnel, en of the limited number of available borings. No geotechnical gineering consultants, building owners and developers, insur data were available in other high liquefaction hazard areas lo ance providers, and private citizens with a relative assessment cated along minor streams and drainages. Consequently, as of the likelihood of soil liquefaction during an earthquake. The sessment of the liquefaction susceptibility is based on the age various data used in the liquefaction susceptibility assessment and geological setting of these deposits. Late Pleistocene ( 12,000-14,000 year old) glaciolacustrine (glacial lake) and glaciofluvial (glacial river) sediments pre Errata dominantly composed of sand and Holocene landslide deposits There are two mistakes on the accompanying map that are are regarded as having a low to moderate liquefaction suscepti explained in the caption of Figure 1 and in the second para bility. Geotechnical analyses using ground-water conditions gaph on page 9. reported at the time of drilling indicate that unit Qvrs deposits 3 4 GEOLOGIC MAP GM-47 Qp Figure 1. Simplified geologic map of the study area generalized from Walsh and others (in press). The darker shaded polygon was inadvertently mislabeled and should be shown as "very low" on the liquefaction susceptibility map. have a low to moderate liquefaction susceptibility. Some of the Quantitative evaluation of geotechnical data obtained from reported occurrences ofliquefaction ground failures during the all other Pleistocene deposits indicates a very low susceptibil 1949 and 1965 Puget Sound earthquakes are located within this ity to liquefaction. The historic