Source parameters for aftershocks of the Oroville, California, earthquake

1984 ◽  
Vol 74 (4) ◽  
pp. 1101-1123
Author(s):  
Jon Fletcher ◽  
John Boatwright ◽  
Linda Haar ◽  
Thomas Hanks ◽  
Art McGarr
Keyword(s):  
Stress Drop ◽  
Dynamic Stress ◽  
Depth Interval ◽  
Causal Mechanism ◽  
Overburden Pressure ◽  
Data Set ◽  
State Of Stress ◽  
Aftershock Sequences ◽  
Least Squares Fit ◽  
Stress Drops

Abstract A suite of 111 strong-motion accelerograms for 14 aftershocks of the Oroville, California, earthquake (ML = 5.7, 1 August 1975) that range in local magnitude (ML) from 2.8 to 5.2 has been analyzed to obtain estimates of seismic moment (Mo), source radius (ro), and stress drop (Δσ) in addition to the focal parameters of location, depth, and fault-plane solution. This data set, which is unusually complete for near-source (Δ ≲ 20 km) on-scale readings, allows for greater precision in the calculation of various measures of stress difference as represented by the Brune stress drop, the apparent stress, the arms stress drop, and the dynamic stress drop. In addition, the seismicity following each aftershock and state-of-stress seem to correlate with particular estimates of stress drop. Seismic moments were calculated from the asymptotic long-period spectral levels which were corrected for the radiation pattern of a double-couple point source. They range from 1.4 × 1021 dyne-cm for a ML = 2.8 shock to 3.3 × 1023 dyne-cm for a ML = 5.1 event. A least-squares fit between ML and the logarithm Mo yields log M 0 = ( 1.36 ± 0.22 ) M L + ( 16.8 ± 1.1 ) for M L ≧ 4.3 and log ⁡ M 0 = ( 1.1 ± 0.14 ) M L + ( 18 ± 0.51 ) for M L ≦ 4.1. These relationships are qualitatively in agreement with the response of the Wood-Anderson instrument to a Brune pulse. Stress drops from the Brune formulation range about 14 to 170 bars. Stress drop is correlated with depth in that the deepest events have the largest stress drops and no large stress drops occur at the shallow depths. Apparent stresses are smaller than the Brune stress drops and show a weaker depth dependence over the depth interval for which they are available. The stress drop calculated from the rms of acceleration (arms) was approximately constant at about 90 bars for 5 of the 7 larger events analyzed; the two high values of 160 and 190 bars were obtained only for the two events which had marked aftershock sequences of their own. These results may be interpreted in terms of the state-of-stress, simple fracture criteria, and mechanisms for the generation of aftershocks. The increase with depth of the envelope of the Brune stress drops may be caused by an increase in shear stress from overburden pressure. Smaller stress drop events can occur at any depth interval. The causal mechanism of aftershocks is not known, but probably includes a change in the frictional properties of the fault, suggesting that the arms stress drop is a measure of the frictional or dynamic stress release.

Stress Drop Mapping in the Northern Chilean Subduction Zone

2020 ◽  
Author(s):  
Jonas Folesky ◽  
Joern Kummerow ◽  
Serge A. Shapiro
Keyword(s):  
Subduction Zone ◽  
Stress Drop ◽  
Observation Interval ◽  
Spectral Ratio ◽  
Temporal Variations ◽  
Data Set ◽  
Systematic Analysis ◽  
Megathrust Earthquakes ◽  
Time Period ◽  
Stress Drops

<p>The Northern Chilean subduction zone has been monitored by the IPOC network for more than ten years. During this time period two very large earthquakes occurred, the 2007 M<sub>W</sub>7.7  Tocopilla earthquake and the 2014 M<sub>W</sub>8.1 Iquique earthquake. Over the entire subduction zone a vast amount of seismic activity has been recorded and a huge catalog was compiled including over 100000 events (Sippl et al. 2018). With this exceptional data base we attempt a systematic analysis of the stress drops of as many events from the catalog as possible. We apply different estimation techniques, namely the spectral ratio type, the spectral stacking approach, and the lower bound method. A goal of our research is a comparison and possibly a combination of the techniques to obtain reliable and well constrained results.</p><p>The data set covers events at the interface, within the subducting plate, crustal events, and intermediate depth events. It therefore bears a great potential to better understand the stress drop distribution within a subduction zone. Also, the long observation interval allows to analyze temporal variations according to pre-, inter-, and post-seismic phases of megathrust earthquakes.   </p><p>We present preliminary results where a subset of 730 events with a magnitude range of M<sub>L</sub>2.7 - M<sub>L</sub>4.8  was used for analysis with the spectral ratio technique. For these events we show maps of spatial stress drop variation, and we analyze the time dependent stress drop variance. </p>

Upper bounds on near-source peak ground motion based on a model of inhomogeneous faulting

1982 ◽  
Vol 72 (6A) ◽  
pp. 1825-1841
Author(s):  
A. McGarr
Keyword(s):  
Ground Motion ◽  
Stress Drop ◽  
Source Region ◽  
Seismic Source ◽  
Theoretical Argument ◽  
Peak Acceleration ◽  
Data Set ◽  
State Of Stress ◽  
Earthquake Size ◽  
Reported Data

abstract Two independent arguments indicate an upper bound of about 10 for the ratio ro/ri in the expressions for peak velocity v and peak acceleration a at close hypocentral distances R: v = (βΔτro/μR)[0.10(ro/ri) + 0.15] and a = (Δτ/ρR)[0.30(ro/ri)2 + 0.45], where ri is the radius of the most heavily loaded asperity that fails within an earthquake source region of radius ro, Δτ is the stress drop, β is the shear-wave velocity, μ is the modulus of rigidity, and ρ is the density; these relationships are for ground motion recorded in a whole-space. First, a recently reported data set was augmented by observations for six earthquakes in the magnitude range 4 ≦ ML ≦ 6.6, for which ground motion was recorded at a minimum of five sites at hypocentral distances of the order of 10 km; the new events include the 1979 Coyote Lake and 1979 Imperial Valley shocks. The entire data set of 22 events, spanning a range in seismic moment from 5 × 1016 to over 1026 dyne-cm, is consistent both with the bound ro/ri < 10 and with the previous conclusion that this ratio does not depend systematically on earthquake size. Second, a theoretical argument, using the result of Savage and Wood that the apparent stress acting on the earthquake fault plane is less than half of the stress drop, is made to the effect that ro/ri < 10. In addition, absolute limits, independent of earthquake size, for peak acceleration are related to the state of stress in the crust; for an extensional state of stress a ≦ 0.40 g and for a compressional stress state a ≦ 2.0 g, where a now represents the maximum horizontal acceleration as recorded at the surface directly above the seismic source.

Stress Drops from Trench to Depth in the Northern Chilean Subduction Zone

2021 ◽  
Author(s):  
Jonas Folesky ◽  
Rens Hofman ◽  
Jörn Kummerow
Keyword(s):  
Subduction Zone ◽  
Stress Drop ◽  
Template Matching ◽  
High Stress ◽  
Spectral Ratio ◽  
Observation Time ◽  
Data Set ◽  
First Results ◽  
Depth Dependency ◽  
Stress Drops

<div> <div> <div> <p>At the northern Chilean subduction zone the IPOC network monitors seismicity since 2007. During the observation time period two very large earthquakes occurred, the 2007 MW 7.7 Tocopilla earthquake and the 2014 MW 8.1 Iquique earthquake and until today the subduction zone shows a vast amount of seismic activity. A large catalog was compiled and published including over 100000 events by Sippl et al. 2018. Therein, seismicity ranges from close to the trench till deep into the mantle to about 300km depth. Consequently, events occur under a broad variability of physical conditions.</p> <p>We extend the aforementioned catalog by applying a template matching technique to identify additional events, that are colocated with catalog events. Based on these events we apply an empirical Green’s function method called spectral ratio approach to estimate stress drops. The results cover different nucleation provinces i.e. the data set includes stress drops obtained at the interface, within the subducting plate, from crustal events, intermediate depth events, and from deep to very deep seismicity. The study therefore bears a great potential to better understand the stress drop distribution within an entire subduction zone.</p> </div> </div> </div><p>First results show no depth dependency in the shallowest 100 km but spatial variability with high stress drops focused to particular regions on the interface. We also find increased stress drop values in the crust when compared to events close or at the interface.</p>

Broadband analysis of the extended foreshock sequence of the Miyagi-Oki earthquake of 12 June 1978

1982 ◽  
Vol 72 (6A) ◽  
pp. 2017-2036
Author(s):  
George L. Choy ◽  
John Boatwright
Keyword(s):  
Stress Drop ◽  
Dynamic Stress ◽  
Main Shock ◽  
Body Waves ◽  
The Third ◽  
Radiated Energy ◽  
Dynamic Stress Drop ◽  
Static Stress Drop ◽  
Stress Drops ◽  
Seismograph Network

abstract The Miyagi-Oki earthquake of 12 June 1978, a large (Ms 7.8) interplate thrust event, occurred in a region which had not experienced earthquakes of magnitude greater than 7 since 1938. A sequence of four moderate-sized (5.4 < mb < 6.1) earthquakes encircled the rupture zone of the Miyagi-Oki earthquake over a period of 2 yr before the main shock. Broadband displacement and velocity records of body waves recorded digitally by stations of the Global Digital Seismograph Network are analyzed to determine the static and dynamic characteristics of the sequence. These characteristics include moment, radiated energy, dynamic and static stress drop, and apparent stress. Inversions of duration measurements made on the velocity waveforms permit quantifying the complexity of an event as well as constraining its rupture geometry. Intervals of 7 to 8 months separated the first three events; the main shock occurred 4 months after the third event. The rupture process of the third event was relatively complex; the event also had a substantially higher dynamic stress drop (175 bars) than did the stress drops of the first two events (9 and 10 bars, respectively). These observations suggest that the third event was an interme-diate-term precursor to the main shock. The fourth event, a short-term precursor to the main shock, occurred about 8 min before the main shock. Its dynamic stress drop (20 bars) was lower than that of the third event but higher than that of the first two events.

scholarly journals MAX-DOAS observations of aerosols, formaldehyde and nitrogen dioxide in the Beijing area: comparison of two profile retrieval approaches

2015 ◽  
Vol 8 (2) ◽  
pp. 941-963 ◽  
Author(s):  
T. Vlemmix ◽  
F. Hendrick ◽  
G. Pinardi ◽  
I. De Smedt ◽  
C. Fayt ◽  
...  
Keyword(s):  
Standard Deviation ◽  
A Priori ◽  
Systematic Bias ◽  
Aerosol Extinction ◽  
Data Set ◽  
Near Surface ◽  
Beijing Area ◽  
Least Squares Fit ◽  
Relative Differences ◽  
Good Agreement

Abstract. A 4-year data set of MAX-DOAS observations in the Beijing area (2008–2012) is analysed with a focus on NO2, HCHO and aerosols. Two very different retrieval methods are applied. Method A describes the tropospheric profile with 13 layers and makes use of the optimal estimation method. Method B uses 2–4 parameters to describe the tropospheric profile and an inversion based on a least-squares fit. For each constituent (NO2, HCHO and aerosols) the retrieval outcomes are compared in terms of tropospheric column densities, surface concentrations and "characteristic profile heights" (i.e. the height below which 75% of the vertically integrated tropospheric column density resides). We find best agreement between the two methods for tropospheric NO2 column densities, with a standard deviation of relative differences below 10%, a correlation of 0.99 and a linear regression with a slope of 1.03. For tropospheric HCHO column densities we find a similar slope, but also a systematic bias of almost 10% which is likely related to differences in profile height. Aerosol optical depths (AODs) retrieved with method B are 20% high compared to method A. They are more in agreement with AERONET measurements, which are on average only 5% lower, however with considerable relative differences (standard deviation ~ 25%). With respect to near-surface volume mixing ratios and aerosol extinction we find considerably larger relative differences: 10 ± 30, −23 ± 28 and −8 ± 33% for aerosols, HCHO and NO2 respectively. The frequency distributions of these near-surface concentrations show however a quite good agreement, and this indicates that near-surface concentrations derived from MAX-DOAS are certainly useful in a climatological sense. A major difference between the two methods is the dynamic range of retrieved characteristic profile heights which is larger for method B than for method A. This effect is most pronounced for HCHO, where retrieved profile shapes with method A are very close to the a priori, and moderate for NO2 and aerosol extinction which on average show quite good agreement for characteristic profile heights below 1.5 km. One of the main advantages of method A is the stability, even under suboptimal conditions (e.g. in the presence of clouds). Method B is generally more unstable and this explains probably a substantial part of the quite large relative differences between the two methods. However, despite a relatively low precision for individual profile retrievals it appears as if seasonally averaged profile heights retrieved with method B are less biased towards a priori assumptions than those retrieved with method A. This gives confidence in the result obtained with method B, namely that aerosol extinction profiles tend on average to be higher than NO2 profiles in spring and summer, whereas they seem on average to be of the same height in winter, a result which is especially relevant in relation to the validation of satellite retrievals.

Seismic quiescence, stress drops, and asperities in the New Hebrides arc

1983 ◽  
Vol 73 (1) ◽  
pp. 219-236
Author(s):  
M. Wyss ◽  
R. E. Habermann ◽  
Ch. Heiniger
Keyword(s):  
High Stress ◽  
Plate Boundary ◽  
Seismic Quiescence ◽  
Data Set ◽  
Seismicity Rate ◽  
Seismic Gaps ◽  
Main Shocks ◽  
Seismicity Rates ◽  
New Hebrides ◽  
Stress Drops

abstract The rate of occurrence of earthquakes shallower than 100 km during the years 1963 to 1980 was studied as a function of time and space along the New Hebrides island arc. Systematic examination of the seismicity rates for different magnitude bands showed that events with mb < 4.8 were not reported consistently over time. The seismicity rate as defined by mb ≧ 4.8 events was examined quantitatively and systematically in the source volumes of three recent main shocks and within two seismic gaps. A clear case of seismic quiescence could be shown to have existed before one of the large main shocks if a major asperity was excluded from the volume studied. The 1980 Ms = 8 rupture in the northern New Hebrides was preceded by a pattern of 9 to 12 yr of quiescence followed by 5 yr of normal rate. This pattern does not conform to the hypothesis that quiescence lasts up to the mainshock which it precedes. The 1980 rupture also did not fully conform to the gap hypothesis: half of its aftershock area covered part of a great rupture which occurred in 1966. A major asperity seemed to play a critical role in the 1966 and 1980 great ruptures: it stopped the 1966 rupture, and both parts of the 1980 double rupture initiated from it. In addition, this major asperity made itself known by a seismicity rate and stress drops higher than in the surrounding areas. Stress drops of 272 earthquakes were estimated by the MS/mb method. Time dependence of stress drops could not be studied because of changes in the world data set of Ms and mb values. Areas of high stress drops did not correlate in general with areas of high seismicity rate. Instead, outstandingly high average stress drops were observed in two plate boundary segments with average seismicity rate where ocean floor ridges are being subducted. The seismic gaps of the central and northern New Hebrides each contain seismically quiet regions. In the central New Hebrides, the 50 to 100 km of the plate boundary near 18.5°S showed an extremely low seismicity rate during the entire observation period. Low seismicity could be a permanent property of this location. In the northern New Hebrides gap, seismic quiescence started in mid-1972, except in a central volume where high stress drops are observed. This volume is interpreted as an asperity, and the quiescence may be interpreted as part of the preparation process to a future large main shock near 13.5°S.

Source dimensions and stress drops of small earthquakes near Parkfield, California

1984 ◽  
Vol 74 (1) ◽  
pp. 27-40
Author(s):  
M. E. O'Neill
Keyword(s):  
Stress Drop ◽  
Small Region ◽  
Static Stress ◽  
Depth Range ◽  
Zero Crossing ◽  
Source Dimensions ◽  
Duration Magnitude ◽  
Short Period ◽  
Static Stress Drop ◽  
Stress Drops

Abstract Source dimensions and stress drops of 30 small Parkfield, California, earthquakes with coda duration magnitudes between 1.2 and 3.9 have been estimated from measurements on short-period velocity-transducer seismograms. Times from the initial onset to the first zero crossing, corrected for attenuation and instrument response, have been interpreted in terms of a circular source model in which rupture expands radially outward from a point until it stops abruptly at radius a. For each earthquake, duration magnitude MD gave an estimate of seismic moment MO and MO and a together gave an estimate of static stress drop. All 30 earthquakes are located on a 6-km-long segment of the San Andreas fault at a depth range of about 8 to 13 km. Source radius systemically increases with magnitude from about 70 m for events near MD 1.4 to about 600 m for an event of MD 3.9. Static stress drop ranges from about 2 to 30 bars and is not strongly correlated with magnitude. Static stress drop does appear to be spatially dependent; the earthquakes with stress drops greater than 20 bars are concentrated in a small region close to the hypocenter of the magnitude 512 1966 Parkfield earthquake.

A dynamic model for far-field acceleration

1982 ◽  
Vol 72 (4) ◽  
pp. 1049-1068
Author(s):  
John Boatwright
Keyword(s):  
Stress Drop ◽  
High Frequency ◽  
Dynamic Stress ◽  
The Body ◽  
Body Waves ◽  
Far Field ◽  
Rupture Velocity ◽  
Frequency Level ◽  
Average Change ◽  
Dynamic Stress Drop

abstract A model for the far-field acceleration radiated by an incoherent rupture is constructed by combining Madariaga's (1977) theory for the high-frequency radiation from crack models of faulting with a simple statistical source model. By extending Madariaga's results to acceleration pulses with finite durations, the peak acceleration of a pulse radiated by a single stop or start of a crack tip is shown to depend on the dynamic stress drop of the subevent, the total change in rupture velocity, and the ratio of the subevent radius to the acceleration pulse width. An incoherent rupture is approximated by a sample from a self-similar distribution of coherent subevents. Assuming the subevents fit together without overlapping, the high-frequency level of the acceleration spectra depends linearly on the rms dynamic stress drop, the average change in rupture velocity, and the square root of the overall rupture area. The high-frequency level is independent, to first order, of the rupture complexity. Following Hanks (1979), simple approximations are derived for the relation between the rms dynamic stress drop and the rms acceleration, averaged over the pulse duration. This relation necessarily depends on the shape of the body-wave spectra. The body waves radiated by 10 small earthquakes near Monticello Dam, South Carolina, are analyzed to test these results. The average change of rupture velocity of Δv = 0.8β associated with the radiation of the acceleration pulses is estimated by comparing the rms acceleration contained in the P waves to that in the S waves. The rms dynamic stress drops of the 10 events, estimated from the rms accelerations, range from 0.4 to 1.9 bars and are strongly correlated with estimates of the apparent stress.

A Source Physics Interpretation of Nonself-Similar Double-Corner-Frequency Source Spectral Model JA19_2S

2022 ◽  
Author(s):  
Chen Ji ◽  
Ralph J. Archuleta
Keyword(s):  
Stress Drop ◽  
Wave Speed ◽  
Dynamic Stress ◽  
Corner Frequency ◽  
Rupture Velocity ◽  
Scaling Relation ◽  
Shear Wave Speed ◽  
Dynamic Stress Drop ◽  
Static Stress Drop ◽  
Frequency Source

Abstract We investigate the relation between the kinematic double-corner-frequency source spectral model JA19_2S (Ji and Archuleta, 2020) and static fault geometry scaling relations proposed by Leonard (2010). We find that the nonself-similar low-corner-frequency scaling relation of JA19_2S model can be explained using the fault length scaling relation of Leonard’s model combined with an average rupture velocity ∼70% of shear-wave speed for earthquakes 5.3 < M< 6.9. Earthquakes consistent with both models have magnitude-independent average static stress drop and average dynamic stress drop around 3 MPa. Their scaled energy e˜ is not a constant. The decrease of e˜ with magnitude can be fully explained by the magnitude dependence of the fault aspect ratio. The high-frequency source radiation is generally controlled by seismic moment, static stress drop, and dynamic stress drop but is further modulated by the fault aspect ratio and the relative location of the hypocenter. Based on these two models, the commonly quoted average rupture velocity of 70%–80% of shear-wave speed implies predominantly unilateral rupture.

An Empirical Method for Dynamic Stress Prediction in Turbomachinery

2009 ◽  
Author(s):  
Timothy C. Allison ◽  
J. Jeffrey Moore
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Dynamic Stress ◽  
Axial Compressor ◽  
Element Model ◽  
Identification Problem ◽  
Empirical Method ◽  
Impulse Response Functions ◽  
Data Set ◽  
Filter Noise

The effectiveness of fatigue and life prediction methods depends heavily on accurate knowledge of the static and dynamic stresses acting on a structure. Although stress fields may be calculated from the finite element shape functions if a finite element model is constructed and analyzed, in many cases the cost of constructing and analyzing a finite element model is prohibitive. Modeling errors can severely affect the accuracy of stress simulations. This paper presents an empirical method for predicting a transient dynamic stress response of a structure based on measured load and strain data that can be collected during vibration tests. The method applies the proper orthogonal decomposition to a measured data set to filter noise and reduce the size of the identification problem and then employs a matrix deconvolution technique to decouple and identify the reduced coordinate impulse response functions for the structure. The method is applied to simulation data from an axial compressor blade model and produces accurate stress predictions compared to finite element results.

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