Source mechanisms for Wilmington Oil Field, California, subsidence earthquakes

1974 ◽  
Vol 64 (3-1) ◽  
pp. 699-711 ◽  
Author(s):  
Robert L. Kovach
Keyword(s):  
Strain Energy ◽  
Focal Depth ◽  
Seismic Source ◽  
Oil Field ◽  
Shear Stresses ◽  
Horizontal Shear ◽  
Amplitude Spectra ◽  
Source Mechanisms ◽  
Stress Drops ◽  
Good Agreement

abstract An unusual set of man-made “earthquakes” was generated in the Wilmington Oil Field, California, during the exploitation of this field. The Wilmington Oil Field was the classic example of an elliptically shaped subsidence bowl produced by the extensive withdrawal of the underlying oil. This surface subsidence produced horizontal shear stresses relieved several times by damaging sudden horizontal movements on very shallow slippage planes. Damaging shocks occurred in 1947, 1949, 1951, 1954, 1955, and 1961. These shocks produced seismograms, primarily composed of surface waves, which present an interesting opportunity to study seismic source mechanisms inasmuch as the focal depth, amount of slip, and source dimensions are known. Rayleigh-wave amplitude spectra for these events reveal seismic moments ranging from 5 × 1022 to 1.7 × 1023 dyne-cm, in good agreement with moments inferred from field observations. A key feature of the subsidence shocks is that very low rupture velocities (0.1 to 0.3 km/sec) were involved. The inferred stress drops indicate that the subsidence shocks must have involved a significant fraction of the available strain energy.

Seismic characteristics of underground nuclear detonations

1971 ◽  
Vol 61 (6) ◽  
pp. 1693-1704
Author(s):  
John R. Murphy ◽  
Richard A. Mueller
Keyword(s):  
Elastic Energy ◽  
Strain Energy ◽  
Seismic Source ◽  
Pressure Profile ◽  
Analytic Approximation ◽  
Poor Agreement ◽  
Radiated Energy ◽  
Energy Equations ◽  
Depth Of Burial ◽  
Good Agreement

abstract An expression is derived for the elastic energy produced by a contained, underground nuclear detonation using an analytic approximation for the pressure profile acting at the elastic radius. The resulting static strain energy and radiated energy equations are evaluated as a function of yield and depth of burial for detonations in tuff and rhyolite. It is shown that, for a given medium, the elastic-energy efficiency depends only on the depth of burial (h) of the device and is proportional to h0.72. Moreover, for the particular scaling relations used, the strain energy shows the same depth dependence as the radiated energy. Seismic-spectrum scaling theory is applied to an analysis of nuclear seismic-source functions, giving results which are in good agreement with the observed differences in the teleseismic magnitude determinations. A magnitude-energy equation is derived for underground nuclear detonations and is noted to be in poor agreement with the Gutenberg-Richter equation. This discrepancy is interpreted to be an indication that the radiated energy from small earthquakes may typically have been underestimated.

The Behaviour of Multiple Loops in Torsion

1988 ◽  
Vol 15 (3) ◽  
pp. 149-156 ◽  
Author(s):  
R. A. Cavina ◽  
N. E. Waters
Keyword(s):  
Energy Method ◽  
Strain Energy ◽  
Vertical Axis ◽  
Experimental Measurements ◽  
Complementary Strain ◽  
Radial Axis ◽  
Strain Energy Method ◽  
Good Agreement

The angular stiffness of a multiple looped span, subject to rotation about a vertical axis (torsion) and also to rotation about a horizontal or radial axis (mesio-distal tilt), have been derived using the complementary (strain) energy method. Experimental measurements on enlarged models were in good agreement with the values calculated from the theoretical relationships obtained. The variations in angular stiffness resulting from changes in the loop height, width, and position of clinical sized loops are discussed.

Dense GPS derived deformation and rotation of intraplate blocks in Central Europe - comparison to seismicity and volcanism

2021 ◽  
Author(s):  
Zhiguo Deng ◽  
Torsten Dahm
Keyword(s):  
High Precision ◽  
Velocity Fields ◽  
Shear Stresses ◽  
Intraplate Seismicity ◽  
Strain Rates ◽  
Horizontal Shear ◽  
Regional Patterns ◽  
Quaternary Volcanism ◽  
Intraplate Deformation ◽  
Horizontal Strain

<p>Intraplate deformation is often small but can nowdays be resolved from high precision GNSS velocity fields derived from decade-long time series and high precision network or point wise  solutions if uncertainties are smaller than ~0.2 mm/a.</p><p>If local effects are discarded, dense velocity fields may resolve regional patterns of intraplate deformation and motion, which are related to the bending of lithospheric plates, to mantle upwelling, the diffuse or zoned deformation along structural weaknesses or faults, and the rotation of rigid blocks within a plate. </p><p>We derive for the first time, dense high precision network solutions at 323 GNSS stations in Germany and adjacent areas and resolve regions experiencing uplift with velocities of up to ~2 mm/a, rotational relative motions with angular velocities of ~0.7±0.3 mas/a, and horizontal shear along an extended,  NS trending zone with strain rates in the range of 10-8 1/a. </p><p>We integrate European dense velocity solutions into our dataset to discuss the geodynamic context to European microplate motions, the Alpine collision, the structure of the European mantle, Quaternary volcanism and historical seismicity. </p><p>Unexpectedly, the zones of high horizontal strain rates only partly correlate to seismicity. Such a non-correlation between ongoing horizontal strain and seismicity has been recognized before. We discuss possible reasons for the absence of intraplate seismicity in regions experiencing recent strain, including the stress shadow effects if the strain buildup is reducing shear stresses from plate tectonics. The combination of GNSS derived dense velocity fields with time dependent seismicity models may change our current understanding of intraplate seismicity and impact the assessment of intraplate seismic hazard in future. </p>

Strong ground motion of mine tremors: Some implications for near-source ground motion parameters

1981 ◽  
Vol 71 (1) ◽  
pp. 295-319
Author(s):  
A. McGarr ◽  
R. W. E. Green ◽  
S. M. Spottiswoode
Keyword(s):  
Ground Motion ◽  
Source Parameters ◽  
Seismic Source ◽  
Shear Velocity ◽  
Recording System ◽  
Ground Acceleration ◽  
Hypocentral Distance ◽  
Earthquake Size ◽  
Mine Tremors ◽  
Stress Drops

abstract Ground acceleration was recorded at a depth of about 3 km in the East Rand Proprietary Mines, South Africa, for tremors with −1 ≦ ML ≦ 2.6 in the hypocentral distance range 50 m < R ≦ 1.6 km. The accelerograms typically had predominant frequencies of several hundred Hertz and peak accelerations, a, as high as 12 g. The peak accelerations show a dependence on magnitude, especially when expressed as dynamic shear-stress differences, defined as σ˜ = ρRa, where ρ is density. For the mine tremors, σ˜ varies from 2 to 500 bars and depends on magnitude according to log σ˜ = 1.40 + 0.38 · ML. Accelerograms for 12 events were digitized and then processed to determine velocity and, for seven events with especially good S/N, displacement and seismic source parameters. Peak ground velocities v ranged up to 6 cm/sec and show a well-defined dependence one earthquake size as measured by ML or by seismic moment, Mo. On the basis of regression fits to the mine data, with −0.76 ≦ ML ≦ 1.45, log Rv = 3.95 + 0.57 ML, where Rv is in cm2/sec, and log Rv = −4.68 + 0.49 log Mo. These regression lines agree excellently with the corresponding data for earthquakes of ML up to 6.4 or Mo to 1.4 × 1026 dyne-cm. At a given value of ML or Mo, a, at fixed R, shows considerably greater variation than v and appears to depend on the bandwidth of the recording system. The peak acceleration at small hypocentral distances is broadly consistent with ρRa = 1.14 Δτrofs/β, where Δτ is stress drop, ro is the source radius, β is shear velocity, and fs is the bandwidth of the recording system. The peak velocity data agree well with Rv = 0.57 βΔτro/μ, where μ is the modulus of rigidity; both expressions follow from Brune's model of the seismic source and were compared with data for events in the size range 5 × 1016 ≦ Mo ≦ 1.4 × 1026 dyne-cm. Measurements of the source parameters indicated that, as for earthquakes, the stress drops for the tremors range from 1 to 100 bars and show no consistent dependence on Mo down to Mo = 5 × 1016 dyne-cm.

Source mechanism of the Truckee, California, earthquake of September 12 1966

1970 ◽  
Vol 60 (4) ◽  
pp. 1199-1208 ◽  
Author(s):  
Yi-Ben Tsai ◽  
Keiiti Aki
Keyword(s):  
Seismic Moment ◽  
Additional Data ◽  
Focal Depth ◽  
P Wave ◽  
Eastern United States ◽  
Time Data ◽  
Travel Time Data ◽  
Amplitude Spectra ◽  
Plane Solution ◽  
Minimum Estimate

abstract With additional data on P wave polarities, the existing fault plane solution for the Truckee, California, earthquake of September 12 1966 (Ryall, Van Wormer and Jones, 1968) is revised to have the following strike and dip angles for its nodal planes: Strike Dip Plane A N 44°E 80°SE Plane B N 134°E 90° Nodal plane A is shown to agree very well with the aftershock zone determined by Greensfelder (1968). The observed Rayleigh and Love wave amplitude spectra from four WWSSN stations in the eastern United States are consistent with the revised solution, but not with the original one by Ryall et al. From these data, the focal depth and seismic moment of the earthquake are determined as 10 km and 0.83 × 1025 dyne-cm, respectively. The focal depth so obtained is the same as that determined from the near station travel time data by Ryall et al. The seismic moment is used to give a minimum estimate of about 30 cm for the average dislocation of the fault.

Effect of Bending Rigidity of Stringers Upon Stress Distribution in Reinforced Monocoque Cylinder Under Concentrated Transverse Loads

1948 ◽  
Vol 15 (1) ◽  
pp. 30-36
Author(s):  
Robert S. Levy
Keyword(s):  
Stress Distribution ◽  
Present Method ◽  
Load Application ◽  
Shear Stresses ◽  
Bending Rigidity ◽  
Work Analysis ◽  
Rigidity Results ◽  
Transverse Loads ◽  
Strain Rosette ◽  
Good Agreement

Abstract Least-work analysis of stress distribution in a reinforced circular monocoque cylinder is extended to determine the effect of bending resistant stringers located at the points of application of concentrated transverse loads. Calculations for a numerical example, with applied loads diametrically opposed, indicate that neglect of stringer bending rigidity results in calculated maximum shear stresses approximately 20 per cent conservative in the fields of load application and 50 per cent unsafe in an intermediate field. Further calculations indicate that the bending rigidity of the stringer has less effect when all loads are applied at the same circumferential location. Comparison of shear stresses, calculated by the present method with strain-rosette readings, indicate good agreement.

scholarly journals Ice-Ocean Interaction On Ronne Ice Shelf, Antarctica

1990 ◽  
Vol 14 ◽  
pp. 341
Author(s):  
A. Jenkins ◽  
C.S.M. Doake
Keyword(s):  
Cold Water ◽  
Sea Water ◽  
Freezing Point ◽  
Accumulation Rate ◽  
Weddell Sea ◽  
Shear Stresses ◽  
Strain Rates ◽  
Horizontal Shear ◽  
Ice Shelf ◽  
Ice Stream

A detailed glaciological study of Ronne Ice Shelf has been undertaken along a flowline extending from Rutford Ice Stream grounding line to the ice front. Measurements of velocity, surface elevation, ice thickness, surface temperature and accumulation rate have been made at a total of 28 sites; at 17 of these ice deformation rates are also known. Although no direct measurements of basal conditions have been made, these can be deduced from observations made at the surface. Assuming the ice shelf to be in a steady state, the basal mass balance can be calculated at points where strain-rates are known. Information on the spatial distribution of basal saline ice layers can also be obtained from radio-echo sounding data. The derived pattern of basal melting and freezing influences both the ice shelf and the underlying ocean. Vertical heat advection modifies the temperature distribution within the ice shelf, which determines its dynamic response to driving and restraining forces through the temperature-dependent ice-flow law. Using measured strain-rates and calculated temperature profiles, the restraint generated by horizontal shear stresses can be derived for points on the flowline. It is the cumulative effect of these forces which controls the discharge of grounded ice from Rutford Ice Stream. Cooling of sea-water to its pressure melting point by melting of ice at depth has two important results. The outflow of cold, dense Ice Shelf Water, produced by this mechanism, is a major source of Antarctic Bottom Water, formed as it mixes at depth with the warmer waters of the Weddell Sea (Foldvik and Gammelsrod, 1988). If the cold water is forced up to shallower depths, frazil ice will be produced as the pressure freezing point rises, resulting in basal accretion if this occurs beneath the ice shelf.

The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting

Geophysics ◽  
2009 ◽  
Vol 74 (5) ◽  
pp. B183-B195 ◽  
Author(s):  
K. De Meersman ◽  
J.-M. Kendall ◽  
M. van der Baan
Keyword(s):  
Seismic Anisotropy ◽  
Amplitude Ratio ◽  
Temporal Variations ◽  
Oil Field ◽  
P Wave ◽  
Wave Form ◽  
S Wave ◽  
Data Set ◽  
Wave Splitting ◽  
Source Mechanisms

We relocate 303 microseismic events recorded in 1998 by sensors in a single borehole in the North Sea Valhall oil field. A semiautomated array analysis method repicks the P- and S-wave arrival times and P-wave polarizations, which are needed to locate these events. The relocated sources are confined predominantly to a [Formula: see text]-thick zone just above the reservoir, and location uncertainties are half those of previous efforts. Multiplet analysis identifies 40 multiplet groups, which include 208 of the 303 events. The largest group contains 24 events, and five groups contain 10 or more events. Within each multiplet group, we further improve arrival-time picking through crosscorrelation, which enhances the relative accuracy of the relocated events and reveals that more than 99% of the seismic activity lies spatially in three distinct clusters. The spatial distribution of events and wave-form similarities reveal two faultlike structures that match well with north-northwest–south-southeast-trending fault planes interpreted from 3D surface seismic data. Most waveform differences between multiplet groups located on these faults can be attributed to S-wave phase content and polarity or P-to-S amplitude ratio. The range in P-to-S amplitude ratios observed on the faults is explained best in terms of varying source mechanisms. We also find a correlation between multiplet groups and temporal variations in seismic anisotropy, as revealed by S-wave splitting analysis. We explain these findings in the context of a cyclic recharge and dissipation of cap-rock stresses in response to production-driven compaction of the underlying oil reservoir. The cyclic nature of this mechanism drives the short-term variations in seismic anisotropy and the reactivation of microseismic source mechanisms over time.

scholarly journals Stability of lubricated viscous gravity currents. Part 1. Internal and frontal analyses and stabilisation by horizontal shear

2019 ◽  
Vol 871 ◽  
pp. 970-1006 ◽  
Author(s):  
Katarzyna N. Kowal ◽  
M. Grae Worster
Keyword(s):  
Viscous Fluid ◽  
Pressure Gradient ◽  
Dynamic Pressure ◽  
Jump Discontinuity ◽  
Local Analysis ◽  
Instability Criterion ◽  
Shear Stresses ◽  
Horizontal Shear ◽  
Dynamical Regimes ◽  
Inner Region

A novel viscous fingering instability, involving a less viscous fluid intruding underneath a current of more viscous fluid, was recently observed in the experiments of Kowal & Worster (J. Fluid Mech., vol. 766, 2015, pp. 626–655). We examine the origin of the instability by asking whether the instability is an internal instability, arising from internal dynamics, or a frontal instability, arising from viscous intrusion. We find it is the latter and characterise the instability criterion in terms of viscosity difference or, equivalently, the jump in hydrostatic pressure gradient at the intrusion front. The mechanism of this instability is similar to, but contrasts with, the Saffman–Taylor instability, which occurs as a result of a jump in dynamic pressure gradient across the intrusion front. We focus on the limit in which the two viscous fluids are of equal density, in which a frontal singularity, arising at the intrusion, or lubrication, front, becomes a jump discontinuity, and perform a local analysis in an inner region near the lubrication front, which we match asymptotically to the far field. We also investigate the large-wavenumber stabilisation by transverse shear stresses in two dynamical regimes: a regime in which the wavelength of the perturbations is much smaller than the thickness of both layers of fluid, in which case the flow of the perturbations is resisted dominantly by horizontal shear stresses; and an intermediate regime, in which both vertical and horizontal shear stresses are important.

On Modeling and Simulation of Innovative Ship Rescue System

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Ilias Zilakos ◽  
Michael Toulios
Keyword(s):  
Strain Energy ◽  
Structural Response ◽  
Dry Land ◽  
Strain Energy Density Function ◽  
Material Evaluation ◽  
Element Simulation ◽  
Rescue System ◽  
Funded Project ◽  
Elasticity Tensors ◽  
Good Agreement

Inflatable devices that provide reserve buoyancy to damaged ships, preventing capsizing and/or sinking, along with lifting wreckages from the seabed, were studied within the framework of the European funded project “SuSy” (Surfacing System for Ship Recovery). Part of the work involved material evaluation and testing as well as simulations of the structural response. This paper first describes an orthotropic hyperelastic constitutive model for a candidate material also used in the fabrication of prototype inflatable devices. A strain energy density function is proposed that is further used to derive the stress and elasticity tensors required for the numerical implementation of the model in the user-defined subroutine (UMAT) of abaqus/standard. The second part of the paper presents the finite element simulation of the latter stages of inflation of two salvage devices inside an actual double bottom structure. The numerical results are in good agreement with tests conducted in dry land and under water, with the structure raised following the inflation of the devices. The evolving stress state in both the devices and the double bottom structure under increased contact interaction leads to useful conclusions for future use in the development of this salvage system.

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