Steven Sobieszczyk | Portland State University (original) (raw)

Papers by Steven Sobieszczyk

AGU Fall Meeting Abstracts, Dec 9, 2019

AGUFM, Dec 1, 2002

Hillsides bordering the Santa Clara ("Silicon") Valley are prone to earthquake- and rai... more Hillsides bordering the Santa Clara ("Silicon") Valley are prone to earthquake- and rainfall-triggered landslides. To narrow the uncertainty surrounding the location of future slope movement, we estimate the relative likelihood of landsliding at 30-m resolution from regional data sets. While small areas are evaluated accurately from detailed observations on material properties, topography, and hydrology, resource limitations force a regional, statistical, approach to mapping large areas. This is the first county-size susceptibility map prepared from the Arc/Info GIS model developed by Pike and others (2001) in the Oakland, CA, area (USGS MF-2385). Their index of susceptibility is the spatial frequency of prior slope failure for each one-degree slope interval in each geologic-map unit, obtained by combining a geologic map (a proxy for rock or soil strength) with a landslide-inventory map and a map of slope gradient. Areas in existing landslides are multiplied by an observationally derived constant, 1.33, to reflect their higher susceptibility. Santa Clara County's 170 geologic units occupy about 3,440,000 30-m grid cells. The geology is from three digital USGS maps (OF 97-710, 98-348, 98-795). The thousands of existing landslides were digitized from 13 inventories--six by the California Geological Survey, five by USGS, two by private consultants. These source maps vary in scale (mostly 1:24,000 or 1:12,000), date (1970-98), attribution of failures (most are large rock and debris slides, rock slumps, and earth flows; few are debris flows), completeness, and detail. The map of slope gradient (OF 98-766) was computed from a 30-m digital elevation model (OF 98-625). Severity of prior landsliding throughout the county strongly reflects geology--from a mean spatial frequency of zero, e.g. flat-lying Pleistocene alluvial fan and fluvial deposits, to 100%, e.g. a mudstone member of the Oligocene-Eocene San Lorenzo Formation. Values of the susceptibility index, ranging from zero (1,000,000 cells largely on the valley floor) to 1.33 (4200 cells in the most hazardous terrain), are not randomly distributed. Among large areas of highest susceptibility (>0.60) are the hills flanking Santa Clara Valley just E of the cities of San Jose, Milpitas, and Morgan Hill, as well as some terrain in the Santa Cruz Mountains.

Geomorphology, Feb 1, 2008

GIS analysis at 30-m resolution reveals that effectiveness of slope-destabilizing processes in th... more GIS analysis at 30-m resolution reveals that effectiveness of slope-destabilizing processes in the San Francisco Bay area varies with compass direction. Nearly half the soil slip/debris flows mapped after the catastrophic rainstorm of 3-5 January 1982 occurred on slopes that face S to WSW, whereas fewer than one-quarter have a northerly aspect. Azimuthal analysis of hillside properties for susceptible terrain near the city of Oakland suggests that the skewed aspect of these landslides primarily reflects vegetation type, ridge and valley alignment, and storm-wind direction. Bedrock geology, soil expansivity, and terrain height and gradient also were influential but less so; the role of surface curvature is not wholly resolved. Normalising soil-slip aspect by that of the region's NNW-striking topography shifts the modal azimuth of soil-slip aspect from SW to SE, the direction of origin of winds during the 1982 storm-but opposite that of the prevailing WNW winds. Wind from a constant direction increases rainfall on windward slopes while diminishing it on leeward slopes, generating a modelled difference in hydrologically effective rainfall of up to 2:1 on steep hillsides in the Oakland area. This contrast is consistent with numerical simulations of wind-driven rain and with rainfall thresholds for debrisflow activity. We conclude that storm winds from the SE in January 1982 raised the vulnerability of the Bay region's many S-facing hillsides, most of which are covered in shallow-rooted shrub and grass that offer minimal resistance to soil slip. Wind-driven rainfall also appears to have controlled debris-flow location in a major 1998 storm and probably others. Incorporating this overlooked influence into GIS models of debris-flow likelihood would improve predictions of the hazard in central California and elsewhere.

Introduction Acknowledgments Oakland's landslide hazard Prior mapping of susceptibility Scope, as... more Introduction Acknowledgments Oakland's landslide hazard Prior mapping of susceptibility Scope, assumptions, method Input to the susceptibility model Geology Old landslide deposits Recent landslides Topography and slope A model of landslide susceptibility Spatial frequency of prior failure Susceptibility between old landslide deposits Susceptibility within old landslide deposits Tests of the susceptibility model The susceptibility map Applications and limitations Future research References cited Appendix-the digital map database Introduction Spatial resolution Overview of the digital database Database contents Revisions Obtaining the database files Opening the database files Importing the ARC export files

Icarus, Sep 1, 2001

We use Monte Carlo methods to simulate impacts of ecliptic comets on the synchronously rotating s... more We use Monte Carlo methods to simulate impacts of ecliptic comets on the synchronously rotating satellites of giant planets. We reconfirm the long-standing prediction that the cratering rate should be much higher on the leading hemispheres than on the trailing hemisphere; indeed we find that previously published analytical formulations modestly underestimate the degree of apexantapex asymmetry to be expected. We then compare our results to new mapping of impact craters on Ganymede, Callisto, and Triton. Ganymede reveals a pronounced apex-antapex asymmetry that is nonetheless much less than predicted. All of Triton's confirmed impact craters are clustered toward the apex of motion, far exceeding the predicted asymmetry. No asymmetry is observed on Callisto. In each case at least one of our basic assumptions must be wrong. Likely candidates include the following: (i) the surfaces of all but the most sparsely cratered satellites are saturated or nearly saturated with impact craters; (ii) these satellites have rotated nonsynchronously over geological time; (iii) most of the craters are made not by heliocentric (Sun-orbiting) comets and asteroids but rather by planetocentric (planet-orbiting) debris of indeterminate origin; or (iv) pathological endogenic resurfacing has created illusions of structure. Callisto's surface is readily classified as nearly saturated. Ganymede's bright terrains, although less heavily cratered than those of Callisto, can also be explained by crater densities approaching saturation on a world where endogenic processes were active. The leading alternative is nonsynchronous rotation, an explanation supported by the distribution of catenae (crater chains produced by impact of tidally disrupted comets). Triton's craters can be explained by planetocentric debris or by capricious resurfacing, but both hypotheses are inherently improbable.

General Information Product

AGU Fall Meeting Abstracts, Dec 14, 2017

Fact Sheet

The U.S. Geological Survey (USGS) operates an extensive nationwide network of stream, rain, and g... more The U.S. Geological Survey (USGS) operates an extensive nationwide network of stream, rain, and groundwater gages. These instruments are used to monitor how much water there is across the Nation at any given moment. How USGS Gages Are Used in Flood Forecasting Stream data are collected at streamgages every 15 minutes, transmitted to USGS servers, and updated online in real time. Different types of stream data are publicly available online, including water level, velocity, and turbidity (how muddy water is). To improve awareness of current water conditions and possible flooding, stream data are combined with rain data collected at nearby USGS rain gages. USGS rain gages are often deployed in remote areas to help confirm the accuracy of weather radar forecasts.

Environmental Modelling & Software, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

From late 2003 through summer 2004, the U.S. Geological Survey's National Water Quality Asses... more From late 2003 through summer 2004, the U.S. Geological Survey's National Water Quality Assessment Program sampled 28 streams within the Willamette Basin to investigate effects of urbanization on aquatic biology (fish, macroinvertebrates and algae), habitat, and water chemistry. The 28 watersheds fall along an urban land use gradient index (0 to 100, lowest to highest) based on land use and

Icarus, 2001

Geomorphology, 2008

Scientific Investigations Report, 2012

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F=(1... more Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F=(1.8×°C)+32. Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25°C). Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or micrograms per liter (µg/L). Algal biomass values are given in milligrams per square meter (mg/m 2). Algal cell density values are given in numbers per square centimeter (#/cm 2). Algal biovolume values are given in cubic micrometers per square centimeter (µ 3 /cm 2). viii Conversion Factors and Datums-Continued Datums Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Elevation, as used in this report, refers to distance above the vertical datum.

Clay-water yields for event periods generally were highest in the Little North Santiam River subb... more Clay-water yields for event periods generally were highest in the Little North Santiam River subbasin. In addition, average annual percentage of clay-water volume during the period of record was highest in the Little North Santiam River. The second highest average was in Blowout Creek.