Site Specific Seismic/Geologic Hazards Risk Zoning

A site specific risk zoning study was conducted on a Junior College Campus near Eureka, California, USA to evaluate the potential seismic/geologic hazards due to the presence of a 1 km wide low angle thrust fault system. Issues addressed to determine the level of risk at any location on the campus include: land sliding, earthquake ground shaking, ground surface rupture and deformation, lateral spreading, liquefaction, differential settlement, and tsunamis. Based on these potential hazards, a micro-zonation model was developed based on 13 different zones and 5 levels of risk. Information for use in this model was collected using a combination of paleo seismic trenches, geophysical surveys and soil borings. This information was then combined to develop a map of risk zones within the campus. This map provides site specific land use recommendations to assist the college in locating appropriate sites for future campus expansion

Seismic Risk Analysis for a Site Along the Gorda Segment of the Cascadia Subduction Zone

A seismic risk evaluation was conducted on a site near Eureka, California. The site was subject to potential earthquake loading from a number of sources. These sources were: (1) Mendocino Fracture Zone, (2) Gorda Segment of the Cascadia Subduction Zone, (3) Little Salmon thrust fault under the site, (4) Mad River Fault Zone, and (5) Intra plate west - Gorda Plate. The geology of thrust faults in Northern California is examined along with that of the Mendocino Fracture Zone, and the southern section (Gorda Segment) of the Cascadia subduction zone. A trench log showing a splay of the Little Salmon Fault is presented. A seismic risk analysis of the site was performed using recurrence curves for the various seismic sources estimated from both trench studies and historic seismicity. Using this information the acceleration at the site due to the Maximum Credible Earthquake is estimated to be 0.85g. The corresponding acceleration due to the Maximum Probable Earthquake and assuming that the various fault zones act independently or co-seismically is estimated to be 0.5g

Compressional and Shear Waves Tests Through Upper Sheet of Low Angle Thrust Fault

Compressional and shear wave tests were conducted on the upper thrust sheet of the low angle Little Salmon thrust fault. The study was conducted on the campus of the College of the Redwoods. The campus is located approximately 8 miles south of Eureka and 24 miles north-northeast of Cape Mendocino and the Mendocino Triple Junction (MTJ) in Northern California. The MTJ is the point of transition from strike-slip faulting of the San Andreas transform system to low-angle reverse (thrust) faulting and folding associated with the convergent margin of the Cascadia Subduction Zone. The campus is located on the southwest limb of the Humboldt Hill anticline, one of the folds in the fold and thrust belt. The Little Salmon fault zone is a low angle thrust fault that day lights on the south side of the campus and then projects underneath striking northwest and dipping northeast. A boring was drilled down to the fault plane located at a depth of 200 ft. in the upper thrust block to develop a mode1 of the stratification as well as the material properties. The boring also revealed the trunk of a redwood tree located at a depth of 180 feet. Results of compressional and shear wave velocities as a function of depth that were determined using an downhole geophysical technique. Results indicated two shear wave velocity units. Unit 1 was from 0 to 120 ft. with a shear wave velocity ranging from 950- 1400 fps. Unit 2 ranged from 120 to 190 ft. with a shear wave velocity ranging from 2300 to 2600 fps. Compression wave velocity measurements obtained from the same test boring also depict a change in velocity in the 100 to 120 foot range. A response spectra was generated based on this in-situ mode1 using SHARE91 and compared against one developed using the Boore, Joyner and Fumal empirical model

Probabilistic Estimation of Site Specific Fault Displacements

The College of the Redwoods (CR) located near Eureka, California would like to upgrade a series of existing buildings that are unfortunately located on secondary faults associated with the active Little Salmon Fault (LSF) zone. In the early 1990’s a deterministic value of the maximum dip-slip displacement that had occurred on one of these secondary faults located beneath the southeast building corner of the former library was measured to be 1.7 feet. This displacement was resolved into approximately 1.5 feet horizontal offset and 0.8 feet of vertical offset, based on the secondary fault plane dip. Geologically, it has not been possible to establish the actual dates of the occurrence of the displacements on the observed faults, therefore it was assumed that they all had occurred within the last 11,000 years. The structural engineer for the project has indicated that it was not possible to design for the observed ground displacement of 1.7 feet. This limited study was undertaken to assess the variation of ground displacements that were observed over the area of ground occupied by CR’s Administration, Science, and former Library buildings. The purpose of this study was to evaluate the reasonableness of using a deterministically determined maximum value of displacement in estimating, and designing mitigations for, the structural response, or whether a probabilistic approach could be utilized. The only data available within the limited time frame allowed for the study was from a series of trench logs made as part of a project for locating building sites on the campus in the early 1990’s. As a first step the frequency distributions of both horizontal and vertical displacements located in a volume of soil comprising the area occupied by the above buildings to a depth of 14 feet were examined. The 14 feet was the maximum depth of the trenches used to provide data for the study. Probability density functions (PDF) versus displacements were developed based on the frequency distributions. The area under the PDF curves between given displacement intervals represents the probability of occurrence (POC) of that displacement. A cumulative probability of occurrence for a displacement interval can be determined by adding the individual POC’s. Based on this it was estimated that a horizontal displacement of ≤ 1.0 foot has a probability of 89% of occurring in the next 11,000 years at the site. In contrast, a vertical displacement of ≤ 1.0 foot has a probability of 88% probability of occurrence

Use of Microzonation to Site Facility on Low Angle Thrust and Associated Fault Bend Folding

The campus of the College of the Redwoods is located completely within the Little Salmon Fault Zone, designated by the State of California as an active fault. The College has been extensively investigated for fault rupture and other seismic hazards in 1989, 1993, 1997, 1998, and 1999. The Little Salmon Fault Zone bounds the College and consists of two main northwest-striking, northeastdipping, low-angle thrusts. The west splay daylights along the southwest edge of the campus and projects beneath it. A recurrence interval of 268 years and slip rate of 5+/-3 mm/yr is estimated by CDMG. Individual dip-slip displacements along the west trace are reported to be 12 to 15 feet (3.6 to 4.5 m). Movement on the Little Salmon fault (LSF) is accompanied by growth of broad asymmetric folds in the upper thrust sheet resulting in surface rupture, localized uplift and discreet fault-bend fold axial surfaces. College of the Redwoods is located approximately 8 miles (13 km) south of Eureka and 25 miles (40 km) north-northeast of Cape Mendocino and the Mendocino Triple Junction (MTJ) in northern California. The \u27MTJ is the point of transition fi-om strike-slip faulting of the San Andreas transform system to low-angle thrust faulting and folding associated with the convergent margin of the Cascadia Subduction Zone. Campus infrastructure is located along the base of the Humboldt Hill Anticline (HHA), a major faultbend fold of the Cascadia fold and thrust belt. A new learning resource center (LRC) is proposed for a location 400 feet (120 m) northeast of where the west trace of the LSF daylights and 200 feet (60 m) above the low-angle fault plane. Building setback and design recommendations to mitigate for both fault rupture hazards and fault-generated folding hazards are presented

On normal networks

Phylogenetic trees have long been the standard object used in evolutionary biology to illustrate how a given set of species are related. Evidence is mounting to suggest that hybridization, historical events when multiple species merge to form new species, are prevalent enough to warrant inclusion into the field. Phylogenetic networks allow for this possibility. In this paper, we discuss normal networks, a specific type of network with desirable tree-like properties. We find tight upper and lower bounds for certain aspects of the networks, including the number of edges, normal edges, hybrid vertices, parents of a vertex, and children of a vertex. We also find tight upper and lower bounds on the number of vertices and edges of specific cases of normal networks, as well as various interesting, related results that lead to these counts. We discuss the tree containment problem, which asks whether a given network contains the information contained within a given tree. We give an algorithm and prove that the tree containment problem for normal networks is solvable in polynomial time. We also discuss new operations on normal networks that are based off of the subtree-pruning and regrafting operation, a standard phylogenetic tree operation. These new operations allow for us to navigate through normal network space, a graph that represents all normal networks with a given set of leaves in which an edge connecting two networks is present if one network can be obtained from the other using exactly one of the operations discussed. We show that these operations connect binary normal network space, the normal network space in which the normal networks have no more than two edges going into or out of each of vertex. These operations on this network space can be used to give better upper bounds on the number of binary normal networks. We show a few of these upper bounds, as well as compare them to upper bounds of trees and regular networks, a type of network that contains normal networks. Finally, we discuss some work that might be pursued based off of the results in this paper.</p