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HomeMy WebLinkAboutMS 05-13; MARCUS MINOR SUBDIVISION; GEOLOGIC RECONNAISSANCE 2701 HIGHLAND DRIVE; 2005-06-01MICHAEL W. HART, ENGINEERING GEOLOGIST GEOLOGIC RECONNAISSANCE. 2701 HIGHLAND DRIVE, CARLSBAD, CALIFORNIA / FOR: ANDREW MARCUS JUNE, 2005 Michael W. Hart Engineering Geologist P.O. Box 261227. San Diego- California- 92196• (858) 578-4672 June 8, 2005 File No. 667-05 Mr. Andrew Marcus C 2701 Highland Drivee arlsbad, California 92008 Subject: Tentative Parcel Map 2701 Highland Drive Carlsbad, California GEOLOGIC RECONNAISSANCE Dear Mr. Marcus: In accordance with our agreement I have completed a geologic reconnaissance of the subject site. The results of the study indicate that the subject parcel is underlain by a Pleistocene marine terrace formation consisting of dense, red-brown sandstone. Published geologic literature as well as geologic mapping for this study indicates that the property is not underlain by an ancient landslide or active fault. In addition, the natural soils underlying the site are classified as low risk in terms of the potential for slope instability. The opportunity to provide consultation services on this project is appreciated. Should you have any questions concerning the following report, please contact the undersigned at your convenience. Very truyou\ Michael W. Hart cc RTIFIED ENGINEERING Engineering Geologist CEG 706 5cc. addressee L File No. 667-2005 2701 Highland Drive Carlsbad, CA GEOLOGIC RECONNAISSANCE TENTATIVE PARCEL MAP, 2701 HIGHLAND DRIVE CARLSBAD, CALIFORNIA Introduction This report presents the results of a geologic reconnaissance for a property located at the intersection of Las Flores Drive and Hillside Drive in Carlsbad, California (Figures 1 & 2). The purpose of this study is to describe the geologic characteristics of the site as well as the potential geologic hazards to which the site may be susceptible. The scope of work included a review of published geologic literature, stereographic pairs of aerial photographs, and geologic mapping of the site. Site Description The site is located at 2701 Hillside Drive in Carlsbad, California and consists of a 0.44 acre - residential property that is to be split into two parcels, A and B. Parcel A contains an existing residence and detached garage. Parcel B located in the southern portion of the property is essentially undeveloped and contains numerous trees and shrubs. The property slopes gently from the northeast to the southwest towards Las Flores Drive. The lowest elevation on the site (approximately 162 feet) is attained at the southwest property corner and the highest elevation of 178 feet occurs at the northeast property corner. Current plans are to eventually develop Parcel B with a single-family residence. Field Work Field work performed for this study consisted of geologic inspection and mapping of natural and man-made bedrock exposures on and near the site utilizing a survey of the site prepared by William E. Billings, Land Surveyor, dated May, 2005. Michael W. Hart, Engineering Geologist 1 File No. 667-2005 2701 Highland Drive Carlsbad, CA General Geology and Soil Conditions The site is located in the western portion of the Peninsular Range geomorphic province characterized by a series of extensive Pleistocene marine terraces developed on gently westward dipping Tertiary sediments. The project is situated on an uplifted Pleistocene marine terrace at elevations between 162 and 178 feet. Underlying the essentially horizontally bedded marine terrace deposits at an estimated depth of 20 to 30 feet are siltstones and sandstones of the Eocene-aged Santiago Formation (Tan and Kennedy, 1996). Because of the depth of this unit beneath the site, it should not be encountered during the contemplated minor grading operations. The Quaternary aged terrace deposits according to Tan and Kennedy (1996) are probably correlatable with the Bay Point Formation of San Diego and consist of well-bedded to massive, red-brown, medium-grained sandstone and cobble conglomerate. Topsoils developed on the Bay Point Formation generally consist of approximately one foot of loose silty sand overlying a weak argillic horizon consisting. of dark brown sandy clay to clayey sand.*Minor fills probably not exceeding a thickness of 2 to 3 feet may also be present along the south and west property lines Geologic Structure Geologic units on the site are not well exposed because of gentle topographic relief and lack of road cuts; however, other projects in the immediate area reveal that the Bay Point Formation is essentially horizontally stratified. Geologic Hazards Potential geologic hazards considered in this report include the potential for surface faulting, liquefaction, seismically induced settlement, landsliding, flooding, and seismic shaking described as follows. Local Faulting: Mapping by Tan and Kennedy (1996) and review of the Fault Map of California, Jennings, (1994) indicates that the site is not underlain by an active fault. In addition, review of stereographic pairs of aerial photographs (USDA, 1953) indicate the site is not traversed by lineaments that would be suggestive of the possible presence of unmapped faults. The Rose Canyon fault is the closest known active fault and is located off-shore approximately 4 miles to the west. Michael W. Hart, Engineering Geologist 2. File No. 667-2005 2701 Highland Drive Carlsbad, CA Regional Faulting and Seismicity: The site will be affected by seismic shaking as a result of earthquakes on major active faults located throughout the southern California area. The nearest of these fault systems, the Rose Canyon fault, is the most significant fault to the site with respect to the potential for seismic activity. Lindvall and Rockwell (1995) have described the Rose Canyon fault system in terms of several segments that each has distinctive earthquake potential. The site lies near the northern end of the Del Mar segment that extends from Del Mar on the south to the vicinity of Oceanside on the north. According to Lindvall and Rockwell (1995), the Mission Bay and Del Mar fault segments are capable of generating M6.4 to M6.6 earthquakes, respectively, with an estimated recurrence time of approximately 720 years for these events and 1800 years for an earthquake event of M6.9 that would result from rupture of both segments concurrently. Such an event could produce peak ground accelerations at the site of approximately 0.5g (Joyner and Boore, 1982). Other active faults, the Elsinore, San Jacintô, and San Andreas Faults lie approximately 25,.45, and 70 miles, respectively, to the east with corresponding estimated peak ground accelerations for Maximum Probable Earthquake events of approximately 0.15g. 0.05g. and 0.03g (Joyner and Boore, 1982). Liquefaction and Seismically Induced Settlement: The natural soils underlying the site consist of moderately dense sediments that comprise late Pleistocene terrace deposits. These soils as well as properly compacted fills are not considered susceptible to seismically induced liquefaction or settlement Landsliding: A study of stereographic pairs of aerial photographs made for this investigation indicates that there is no geomorphic evidence to suggest the presence of ancient deep-seated landsliding on or adjacent to the site. The site lies in an area of very low topographic relief. This, coupled with the fact that the site is underlain by competent Pleistocene bedrock of the Bay Point Formation, indicates the potential for future landsliding is very low. Flooding: The site does not lie near a source of potential flooding, such as a major body of water or major natural drainage. Therefore, the flooding potential is considered essentially nil. Michael W. Hart, Engineering Geologist 3 File No. 667-2005 2701 Highland Drive Carlsbad, CA Groundwater: No seepage or other evidence of groundwater was observed during the geologic reconnaissance and site inspection. The depth to the regional groundwater surface is unknown, however, the proposed building pad will not likely be excavated to depths where it could be reasonably anticipated that the regional groundwater level would be intercepted. It is possible that seasonal or permanent perched groundwater could occur in cut slopes as a result of irrigation or rainfall and that if basements are constructed, surface water percolating through the sandy surficial soils could accumulate near the basement floor and walls. CONCLUSIONS AND RECOMMENDATIONS The site is primarily underlain by Pleistocene terrace deposits consisting of medium-grained red brown sandstone and conglomerate. These soils may be overlain locally by shallow undocumented fill. Portions of the topsoils may consist of expansive sandy clay. Future foundations should be designed accordingly following the recommendations of a geotechnical engineer. The closest active fault to the property is the Rose Canyon fault that lies offshore approximately 4 miles to the west. A study of aerial photographs and geologic mapping for this site indicates that there is no evidence of ancient landsliding on the property. Similarly, the bedrock units exposed on-site and adjacent properties are not considered landslide prone. Limitations This report has been prepared exclusively for the use of the Client, and is not intended to be relied upon by any other entities or persons. The purpose and intent of this report is to address geologic conditions and the potential for the site to be impacted by geologic hazards. Foundation design parameters related to soil characteristics and grading recommendations are beyond the scope of a geologic reconnaissance. Such recommendations are included in the project geotechnical report. The findings of this report are valid as of the present date. However, changes in the conditions of a property can occur with the passage of time, whether they be due to natural processes or the works of man on this or adjacent properties. In addition, changes in applicable or appropriate standards may occur, whether they result from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside the control of this consultant. Therefore, this report is subject to review and should not be relied upon after a period of three years.. Michael W. Hart, Engineering Geologist 4 File No. 667-2005 2701 Highland Drive Carlsbad, CA References Anderson, I. 0., Rockwell, T., and Agnew, D.C., 1989, A study of the seismic hazard in San Diego, Earthquake Spectra, vol. 5(2), pp 229-333. Jennings, C.W., 1994, Fault activity map of California and adjacent areas with locations and ages of recent volcanic eruptions, Calif. Div. Mines and Geology Geologic Data Map No. 6. Joyner, W.B. and Boore, D.M. 1982, Prediction of earthquake response spectra, U.S. Geological Survey Open File Report 82-977, I6pp. 0 Lindvall, S.C., Rockwell, T.K., and Lindvall, C.E., 1990, The seismic hazard of San Diego revised: New evidence of Magnitude 6+ Holocene earthquakes on the Rose Canyon Fault Zone, in Proceedings of U.S. National Conference on Earthquake Engineering, Palm Springs, California, vol 1: Earthquake Engineering Research Inst., p. 679-688. Lindvall, S.C., and Rockwell, T.K., 1995, Holocene activity of the Rose Canyon fault zone in San Diego, California, Jour. Geophysical Research, vol. 100, no. 812, Pages 24,121-24-132. Tan, S.S., and Kennedy, M.P., 1996, Geologic maps of the northwestern part of San Diego County, California, P1.1, Calif. Div. Mines and Geology, DMG open-File Report 96-02. Treiman, J.A., 1993, The Rose Canyon Fault Zone, southern California, California Div. Mines and Geology, Open File• Report 93-02. Weber, F. H. Jr., 1982, Recent slope failures, ancient landslides, and related geology of the north-central coastal area, San Diego County California, Calif. Div. Mines and Geology Open-File Rept 82-12 LA, pp. 1-77. Michael W. Hart, Engineering Geologist