Geology topics
Eric L. Geist
Publications and source records attributed to Eric L. Geist.
Seaside, Oregon, Tsunami Pilot Study— Modernization of FEMA flood hazard maps: GIS data
Introduction: The Federal Emergency Management Agency (FEMA) Federal Insurance Rate Map (FIRM) guidelines do not currently exist for conducting and incorporating tsunami hazard assessments that reflect the substantial advances in tsunami research achieved in the last two decades; this conclusion is the result of two FEMA-sponsored workshops and the associated Tsunami Focused Study (Chowdhury and others, 2005). Therefore, as part of FEMA's Map Modernization Program, a Tsunami Pilot Study was carried out in the Seaside/Gearhart, Oregon, area to develop an improved Probabilistic Tsunami Hazard Analysis (PTHA) methodology and to provide recommendations for improved tsunami hazard assessment guidelines (Tsunami Pilot Study Working Group, 2006). The Seaside area was chosen because it is typical of many coastal communities in the section of the Pacific Coast from Cape Mendocino to the Strait of Juan de Fuca, and because State agencies and local stakeholders expressed considerable interest in mapping the tsunami threat to this area. The study was an interagency effort by FEMA, U.S. Geological Survey, and the National Oceanic and Atmospheric Administration (NOAA), in collaboration with the University of Southern California, Middle East Technical University, Portland State University, Horning Geoscience, Northwest Hydraulics Consultants, and the Oregon Department of Geological and Mineral Industries. We present the spatial (geographic information system, GIS) data from the pilot study in standard GIS formats and provide files for visualization in Google Earth, a global map viewer.
Triggering of tsunamigenic aftershocks from large strike‐slip earthquakes: Analysis of the November 2000 New Ireland earthquake sequence
[1] The November 2000 New Ireland earthquake sequence started with a M w = 8.0 left‐lateral main shock on 16 November and was followed by a series of aftershocks with primarily thrust mechanisms. The earthquake sequence was associated with a locally damaging tsunami on the islands of New Ireland and nearby New Britain, Bougainville, and Buka. Results from numerical tsunami‐propagation models of the main shock and two of the largest thrust aftershocks ( M w > 7.0) indicate that the largest tsunami was caused by an aftershock located near the southeastern termination of the main shock, off the southern tip of New Ireland (Aftershock 1). Numerical modeling and tide gauge records at regional and far‐field distances indicate that the main shock also generated tsunami waves. Large horizontal displacements associated with the main shock in regions of steep bathymetry accentuated tsunami generation for this event. Most of the damage on Bougainville and Buka Islands was caused by focusing and amplification of tsunami energy from a ridge wave between the source region and these islands. Modeling of changes in the Coulomb failure stress field caused by the main shock indicate that Aftershock 1 was likely triggered by static stress changes, provided the fault was on or synthetic to the New Britain interplate thrust as specified by the Harvard CMT mechanism. For other possible focal mechanisms of Aftershock 1 and the regional occurrence of thrust aftershocks in general, evidence for static stress change triggering is not as clear. Other triggering mechanisms such as changes in dynamic stress may also have been important. The 2000 New Ireland earthquake sequence provides evidence that tsunamis caused by thrust aftershocks can be triggered by large strike‐slip earthquakes. Similar tectonic regimes that include offshore accommodation structures near large strike‐slip faults are found in southern California, the Sea of Marmara, Turkey, along the Queen Charlotte fault in British Columbia, and near the Alpine fault of New Zealand. Results from this study and previous stress modeling studies suggest that the likelihood of local tsunamis in these regions may significantly increase after a great strike‐slip earthquake.
Local tsunami hazards in the Pacific Northwest from Cascadia subduction zone earthquakes
No abstract available.
Effect of structural heterogeneity and slip distribution on coseismic vertical displacement from rupture on the Seattle Fault
Workshops in 2001 and 2002 were convened to determine critical issues in the development of tsunami inundation maps for the Puget Sound region. The Tsunami Inundation Mapping Effort (TIME) is conducted under the multi-agency National Tsunami Hazard Mitigation Program (NTHMP). The Puget Sound Tsunami/Landslide Workshop in 2001 focused on integrated tsunami research involving a wide range of research studies and tsunami hazard mitigation issues. The 2002 Puget Sound Tsunami Sources workshop (González et al., 2003) made specific recommendations for tsunami source modeling and improving our state of knowledge for sources in the Puget Sound region. One of the recommendations stated in González et al. (2003) is "Develop methods to assess the sensitivity of coastal areas to tsunami inundation, based on multiple simulations that reflect the possible range of variations in the source parameters." Tsunami inundation models rely heavily on the imposed initial conditions which, for an earthquake source, is the coseismic vertical displacement field. For example, Koshimura et al. (2002) use the geologic uplift observations (Buknam et al., 1992) to constrain the slip distribution for the event that occurred 1100 years ago, resulting in an average slip of 3.7 m and a magnitude of 7.6. Walsh et al. (2003) develop a tsunami inundation map for Elliot Bay based on a M 7.3 earthquake and the geologic uplift observations from the 1100 y.b.p. event as in Koshimura et al. (2002), though they use a constant fault dip of 60° rather than different dips for deep and shallow segments. The objective of this report is to examine how coseismic vertical displacement from a smaller M 6.5 Seattle Fault earthquake (as in Hartzell et al., 2002) is affected by structural heterogeneity and different slip distribution patterns.
Comments on potential geologic and seismic hazards affecting coastal Ventura County, California
This report examines the regional seismic and geologic hazards that could affect proposed liquefied natural gas (LNG) facilities in coastal Ventura County, California. Faults throughout this area are thought to be capable of producing earthquakes of magnitude 6.5 to 7.5, which could produce surface fault offsets of as much as 15 feet. Many of these faults are sufficiently well understood to be included in the current generation of the National Seismic Hazard Maps; others may become candidates for inclusion in future revisions as research proceeds. Strong shaking is the primary hazard that causes damage from earthquakes and this area is zoned with a high level of shaking hazard. The estimated probability of a magnitude 6.5 or larger earthquake (comparable in size to the 2003 San Simeon quake) occurring in the next 30 years within 30 miles of Platform Grace is 50-60%; for Cabrillo Port, the estimate is a 35% likelihood. Combining these probabilities of earthquake occurrence with relationships that give expected ground motions yields the estimated seismic-shaking hazard. In parts of the project area, the estimated shaking hazard is as high as along the San Andreas Fault. The combination of long-period basin waves and LNG installations with large long-period resonances potentially increases this hazard.
Preliminary hydrodynamic analysis of landslide-generated waves in Tidal Inlet, Glacier Bay National Park, Alaska
A landslide block perched on the northern wall of Tidal Inlet, Glacier Bay National Park (Figure 1), has the potential to generate large waves in Tidal Inlet and the western arm of Glacier Bay if it were to fail catastrophically. Landslide-generated waves are a particular concern for cruise ships transiting through Glacier Bay on a daily basis during the summer months. The objective of this study is to estimate the range of wave amplitudes and periods in the western arm of Glacier Bay from a catastrophic landslide in Tidal Inlet. This study draws upon preliminary findings of a field survey by Wieczorek et al. (2003), and evaluates the effects of variations in landslide source parameters on the wave characteristics.
Helping coastal communities at risk from tsunamis: the role of U.S. Geological Survey research
In 1946, 1960, and 1964, major tsunamis (giant sea waves usually caused by earthquakes or submarine landslides) struck coastal areas of the Pacific Ocean. In the U.S. alone, these tsunamis killed hundreds of people and caused many tens of millions of dollars in damage. Recent events in Papua New Guinea (1998) and elsewhere are reminders that a catastrophic tsunami could strike U.S. coasts at any time. The USGS, working closely with NOAA and other partners in the National Tsunami Hazard Mitigation Program, is helping to reduce losses from tsunamis through increased hazard assessment and improved real-time warning systems.
Local tsunamis and earthquake source parameters
This chapter establishes the relationship among earthquake source parameters and the generation, propagation, and run-up of local tsunamis. In general terms, displacement of the seafloor during the earthquake rupture is modeled using the elastic dislocation theory for which the displacement field is dependent on the slip distribution, fault geometry, and the elastic response and properties of the medium. Specifically, nonlinear long-wave theory governs the propagation and run-up of tsunamis. A parametric study is devised to examine the relative importance of individual earthquake source parameters on local tsunamis, because the physics that describes tsunamis from generation through run-up is complex. Analysis of the source parameters of various tsunamigenic earthquakes have indicated that the details of the earthquake source, namely, nonuniform distribution of slip along the fault plane, have a significant effect on the local tsunami run-up. Numerical methods have been developed to address the realistic bathymetric and shoreline conditions. The accuracy of determining the run-up on shore is directly dependent on the source parameters of the earthquake, which provide the initial conditions used for the hydrodynamic models.
Relationship between the present-day stress field and plate boundary forces in the Pacific Northwest
The relationship between plate boundary forces and the observed stress field in the Pacific Northwest is established using numerical models of continental deformation. Because the orientation of the greatest horizontal principal stress throughout the Pacific Northwest differs considerably from the direction of convergence between the Juan de Fuca and North American plates, the relationship between the stress field and forces acting along the subduction zone has been unclear. To address this relationship, a two‐dimensional finite element model developed by Bird [1989] is used that incorporates critical aspects of continental deformation such as a stratified rheology and interaction between thermal and mechanical components of deformation. Boundary conditions are specified in terms of either velocity or shear traction, depending on whether the computed shear stress at the plate boundary is less than or exceeds, respectively, a prescribed limit. Shear‐stress limits on the subduction and transform plate boundaries are independently varied to determine the relative effect of forces along these boundaries on intraplate deformation. Results from this study indicate that the shear stress limit of both subduction and transform boundaries is low, and that the intraplate stress field is attributed, in part, to the normal component of relative plate motion along the transform boundaries. However, the models also indicate that although the subduction zone fault is weak, a minimum shear strength (≥ 10 MPa) for the fault is necessary to explain the observed stress field. The balance among forces along the tectonic boundaries of North America results in a surprising degree of variation in the present‐day stress field.
Source parameters controlling the generation and propagation of potential local tsunamis along the cascadia margin
The largest uncertainty in assessing hazards from local tsunamis along the Cascadia margin is estimating the possible earthquake source parameters. We investigate which source parameters exert the largest influence on tsunami generation and determine how each parameter affects the amplitude of the local tsunami. The following source parameters were analyzed: (1) type of faulting characteristic of the Cascadia subduction zone, (2) amount of slip during rupture, (3) slip orientation, (4) duration of rupture, (5) physical properties of the accretionary wedge, and (6) influence of secondary faulting. The effect of each of these source parameters on the quasi-static displacement of the ocean floor is determined by using elastic three-dimensional, finite-element models. The propagation of the resulting tsunami is modeled both near the coastline using the two-dimensional ( x-t ) Peregrine equations that includes the effects of dispersion and near the source using the three-dimensional ( x-y-t ) linear long-wave equations. The source parameters that have the largest influence on local tsunami excitation are the shallowness of rupture and the amount of slip. In addition, the orientation of slip has a large effect on the directivity of the tsunami, especially for shallow dipping faults, which consequently has a direct influence on the length of coastline inundated by the tsunami. Duration of rupture, physical properties of the accretionary wedge, and secondary faulting all affect the excitation of tsunamis but to a lesser extent than the shallowness of rupture and the amount and orientation of slip. Assessment of the severity of the local tsunami hazard should take into account that relatively large tsunamis can be generated from anomalous ‘tsunami earthquakes’ that rupture within the accretionary wedge in comparison to interplate thrust earthquakes of similar magnitude.
Origin, transport, and emplacement of an exotic island-arc terrane exposed in eastern Kamchatka, Russia
The regional stratigraphy of eastern Kamchatka includes an exotic, Early-Late Cretaceous ophiolite and Late Cretaceous island-arc volcanic sequence. Integrating the existing geologic and geophysical data, we examine the origin, transport, emplacement, and postemplacement deformation of the island-arc terrane, which is named the Olyutorsky island arc. Results from several paleomagnetic studies consistently indicate that the island-arc terrane originated >1000 km to the south of where it is presently exposed. Although the formative paleolatitudes of the island-arc rocks approximately correspond to the location of the Izanagi-Farallon subduction zone, the age of the volcanic rocks postdates the cessation of Izanagi-Farallon convergence, thus indicating that an unnamed plate or back-arc basin existed in the northwest Pacific during Late Cretaceous time. We examine two possible models for northward transport of the island-arc terrane to Kamchatka: (1) infra-oceanic transport with the Pacific or Kula plates and (2) coastwise translation of the island-arc terrane after accretion to the Eurasian margin far to the south of Kamchatka. For both models, the dominant Eocene and Miocene deformation ages observed in eastern Kamchatka are used as two possible age limits for the cessation of northward transport. Although the observed paleolatitudes from paleomagnetic data correspond best with the infra-oceanic transport model, the provenance of the Paleogene "transport" stratigraphy indicates a near-shore sediment supply. Our preferred interpretation is that the island-arc terrane (1) accreted onto the Eurasian margin concurrent with cessation of island-arc volcanism (Maastrichtian-Danian) and (2) underwent northward coastwise translation along a major strike-slip fault zone ending by middle-late Eocene time (43-50 Ma). It is unclear whether the ophiolite was exposed during arc-continent collision or whether the ophiolite was obducted onto the island arc prior to collision. A consequence of either infra-oceanic transport or coastwise translation is that an open corridor between the western terminus of the Aleutian Arc and Kamchatka must have existed until middle to late Eocene time. Spreading within the Komandorsky Basin, subduction of sea-mounts, and collision of the Aleutian Arc with Kamchatka are proposed to have instigated the second Miocene phase of deformation, which uplifted and reexposed the island-arc terrane.
Field testing the Wildlink Capture Collar on wolves
Seventeen Wildlink capture collars were tested 61 times on 18 gray wolves ( Canis lupus ) during 1989-1991 in the Superior National Forest of northeastern Minnesota. Overall success rate was 89%, and most failures were attributable to premature battery expiration. When batteries were changed ≤ every 2 months, 17 of 17 tests succeeded. With an upgraded version of the collar in which batteries lasted longer, 17 of 18 tests succeeded. Over the 2-year study, 6 of the 17 collars were lost. For serially recapturing individuals, the Wildlink collar proved useful and reliable if care was taken to replace batteries at proper intervals.
Seismic stratigraphy and structure of Prydz Bay, Antarctica: Implications from Leg 119 drilling
Prydz Bay is situated on the MacRobertson Land coast of East Antarctica at the seaward end of a 700-km-long transverse rift zone, the Lambert Rift. New and reprocessed seismic reflection data are combined with drilling results from five Leg 119 sites across Prydz Bay to study the regional stratigraphy and structure of the continental shelf and upper slope. Severe seismic multiples hamper interpretations, yet seven acoustic units separated by unconformities can be distinguished regionally. Only four units (sedimentary) have been drilled. More than 5 km of well- to poorly-stratified units beneath the inner shelf fill the northeast-trending Prydz Bay basin, which is related to, but separated from, the Lambert Graben. Basinal units overlie metamorphic basement (unit PS.5) and are continental nonmarine deposits of possible late Paleozoic to early Mesozoic age (unit PS.4, Site 740) and Early Cretaceous and younger(?) age (unit PS.2B, Site 741). Seaward, the basin is flanked by a buried and intruded(?) basement ridge (units PS.5 and PS.6). Continuous to distorted reflections cover the ridge and dip seaward in a prograding unit (unit PS.2A) beneath the outer shelf. Glaciomarine rocks of late Eocene to early Oligocene age comprise the innermost part of the unit PS.2A (Sites 742 and 739) and Holocene glacial rocks the outermost (Site 743); ages of intermediate parts of the unit are unknown. A flatlying unit of chaotic to continuous reflectors directly beneath the seafloor covers most of the northeast shelf (unit PS. 1, Sites 740, 741, 742, and 739), and is composed of compacted glacial diamictites of late Miocene and younger age. We suspect that significant rifting and glacial events have caused acoustic disconformities beneath Prydz Bay. The principal rifting events began with earliest rifting of Gondwana in late Paleozoic time (units PS.5 to PS.4) and culminated with continental breakup in Early Cretaceous time (units PS.4 to PS.2B). The advent of East Antarctic glaciation in late Eocene to early Oligocene time (units PS.2B to PS.2A) and the grounding of ice sheets across the shelf in midand late-Cenozoic times (unit PS.l to underlying units) created the principal glacial disconformities. The seaward-prograding glacial sequences beneath the outermost shelf record numerous post-early Oligocene glacial events and likely sea-level changes that can only be partially mapped with existing seismic and drilling data.