An official website of the United States government
Seismic isolation systems for buildings are generally selected to achieve higher seismic performance objectives, such as continued operation or immediate occupancy following a design earthquake event. However, recent large scale tests have suggested that these objectives may be compromised if the shaking includes large vertical acceleration components that are damaging to the nonstructural components and contents. Some research has been conducted to develop three dimensional isolation systems that can isolate the structure from both the horizontal and vertical components of ground motion. In several cases, systems have been proposed without much justification of the target design parameters. Rocking has been noted as a potential concern for structures with 3D isolation systems, and complex systems have been proposed to control the rocking. In this study, the fundamental dynamic response of structures with 3D isolation systems is explored. Target horizontal and vertical spectra for a representative strong motion site were developed based on NEHRP recommendations, and horizontal and vertical ground motions were selected that best fit the target spectra when the same amplitude scale factor was applied to all three motion components. Using a simple model of a rigid block resting on linear isolation bearings, the following aspects are evaluated for a wide range of horizontal and vertical isolation periods: response modes and severity of rocking, horizontal and vertical displacement demands in the isolation bearings, and attenuation of both horizontal and vertical accelerations in the structure relative to the ground acceleration. Preliminary results point to a number of useful observations. For example, rocking appears to be an issue only if the horizontal and vertical isolation periods are closely spaced. Helical spring isolation systems that have been applied to a few structures have this characteristic. However, if the horizontal isolation period is large relative to the vertical isolation period, troublesome rocking can be avoided. In addition, other researchers have proposed systems with vertical isolation periods on the order of 2 seconds, which require large displacement and damping capacity. However, preliminary results suggest that vertical isolation periods as low as 0.5 seconds will be effective in attenuating the vertical acceleration. Limiting the vertical isolation period will make design of a 3D isolation system more feasible with respect to vertical displacement capacity and avoiding rocking.
more »
« less
Radial interpolation of GPS and leveling data of ground deformation in a resurgent caldera: application to Campi Flegrei (Italy)
Abstract This study presents a new method, called the Radial Interpolation Method, to interpolate data characterized by an approximately radial pattern around a relatively constrained central zone, such as the ground deformation patterns shown in many active volcanic areas. The method enables the fast production of short-term deformation maps on the base of spatially sparse ground deformation measurements and can provide uncertainty quantification on the interpolated values, fundamental for hazard assessment purposes and deformation source reconstruction. The presented approach is not dependent on a priori assumptions about the geometry, location and physical properties of the source, except for the requirement of a locally radial pattern, i.e., allowing multiple centers of symmetry. We test the new method on a synthetic point source example, and then, we apply the method to selected time intervals of real geodetic data collected at the Campi Flegrei caldera during the last 39 years, including examples of leveling, Geodetic Precise Traversing measurements and Global Positioning System. The maps of horizontal displacement, calculated inland, show maximum values lying along a semicircular annular region with a radius of about 2–3 km in size. This semi-annular area is marked by mesoscale structures such as faults, sand dikes and fractures. The maps of vertical displacement describe a linear relation between the maximum vertical uplift measured and the volume variation. The multiplicative factor in the linear relation is about 0.3 × 10 6 m 3 /cm if we estimate the proportion of the Δ V that is captured by the GPS network onland and we use this to estimate the full Δ V . In this case, the 95% confidence interval on K because of linear regression is ± 5%. Finally, we briefly discuss how the new method could be used for the production of short-term vent opening maps on the base of real-time geodetic measurements of the horizontal and vertical displacements.
more »
« less
- Award ID(s):
- 1821311
- PAR ID:
- 10284996
- Date Published:
- Journal Name:
- Journal of Geodesy
- Volume:
- 94
- Issue:
- 2
- ISSN:
- 0949-7714
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
We investigate the influence of earthquake source characteristics and geological site parameters on fault scarp morphologies for thrust and reverse fault earthquakes using geomechanical models. A total of 3434 distinct element method (DEM) model experiments were performed to evaluate the impact of the sediment depth, density, homogeneous and heterogeneous sediment strengths, fault dip, and the thickness of unruptured sediment above the fault tip on the resultant coseismic ground surface deformation for a thrust or reverse fault earthquake. A machine learning model based on computer vision (CV) was applied to obtain measurements of ground surface deformation characteristics (scarp height, uplift, deformation zone width, and scarp dip) from a total of 346,834 DEM model stages taken every 0.05 m of slip. The DEM dataset exhibits a broad range of scarp behaviors, generating monoclinal, pressure ridge, and simple scarps—each of which can be modified by hanging wall collapse. The parameters that had the most influence on surface rupture patterns are fault displacement, fault dip, sediment depth, and sediment strength. The DEM results comprehensively describe the range of historic surface rupture observations in the Fault Displacement Hazards Initiative (FDHI) dataset with improved relationships obtained by incorporating additional information about the earthquake size, fault geometry, and surface deformation style. We suggest that this DEM dataset can be used to supplement field data and help forecast patterns of ground surface deformation in future earthquakes given specific anticipated source and site characteristics.more » « less
-
Abstract Quantifying off-fault deformation in the near field remains a challenge for earthquake monitoring using geodetic observations. We propose an automated change detection strategy using geometric primitives generated using a deep neural network, random sample consensus and least squares adjustment. Using mobile laser scanning point clouds of vineyards acquired after the magnitude 6.0 2014 South Napa earthquake, our results reveal centimeter-level horizontal ground deformation over three kilometers along a segment of the West Napa Fault. A fault trace is detected from rows of vineyards modeled as planar primitives from the accumulated coseismic response, and the postseismic surface displacement field is revealed by tracking displacements of vineyard posts modeled as cylindrical primitives. Interpreted from the detected changes, we summarized distributions of deformation versus off-fault distances and found evidence of off-fault deformation. The proposed framework using geometric primitives is shown to be accurate and practical for detection of near-field off-fault deformation.more » « less
-
ABSTRACT As part of the 2022 revision of the Aotearoa New Zealand National Seismic Hazard Model (NZ NSHM 2022), deformation models were constructed for the upper plate faults and subduction interfaces that impact ground-shaking hazard in New Zealand. These models provide the locations, geometries, and slip rates of the earthquake-producing faults in the NZ NSHM 2022. For upper plate faults, two deformation models were developed: a geologic model derived directly from the fault geometries and geologic slip rates in the NZ Community Fault Model version 1.0 (NZ CFM v.1.0); and a geodetic model that uses the same faults and fault geometries and derives fault slip-deficit rates by inverting geodetic strain rates for back slip on those specified faults. The two upper plate deformation models have similar total moment rates, but the geodetic model has higher slip rates on low-slip-rate faults, and the geologic model has higher slip rates on higher-slip-rate faults. Two deformation models are developed for the Hikurangi–Kermadec subduction interface. The Hikurangi–Kermadec geometry is a linear blend of the previously published interface models. Slip-deficit rates on the Hikurangi portion of the deformation model are updated from the previously published block models, and two end member models are developed to represent the alternate hypotheses that the interface is either frictionally locked or creeping at the trench. The locking state in the Kermadec portion is less well constrained, and a single slip-deficit rate model is developed based on plate convergence rate and coupling considerations. This single Kermadec realization is blended with each of the two Hikurangi slip-deficit rate models to yield two overall Hikurangi–Kermadec deformation models. The Puysegur subduction interface deformation model is based on geometry taken directly from the NZ CFM v.1.0, and a slip-deficit rate derived from published geodetic plate convergence rate and interface coupling estimates.more » « less
-
Abstract I employ an elasticity‐based method to invert a geodetically derived surface velocity field in the western US using for present‐day surface strain rate fields with uncertainties. The method uses distributed body forces in a thin elastic sheet and allows for discontinuities in velocity across creeping faults using the solution for dislocations in a thin elastic plate. I compare the strain rate fields with previously published stress orientations and moment rates from geological slip rate data and previous geodetic studies. Geologic and geodetic moment rates are calculated using slip rate and off‐fault strain rates from the 2023 US National Seismic Hazard Model (NSHM) deformation models. I find that computed total geodetic moment rates are higher than NSHM summed moment rates on faults for all regions of the western US except the highest deforming rate regions including the Western Transverse Ranges and the northern and southern San Andreas Fault (SAF) system in California. Computed geodetic moment rates are comparable to the moment rates derived from the geodetically based NSHM deformation models in all regions. I find systematic differences in orientations of maximum horizontal shortening rate and maximum horizontal compressive stress in the Pacific Northwest region and along much of the SAF system. In the Pacific Northwest, the maximum horizontal stress orientations are rotated counterclockwise 40–90° relative to the maximum horizontal strain rate directions. Along the SAF system, the maximum horizontal stresses are rotated systematically 25–40° clockwise (closer to fault normal) relative to the strain rates.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s00190-020-01355-x
