Relationship Between Seismic Moment and Source Duration for Seismogenic Earthquakes in Taiwan: Implications for the Product of Static Stress Drop and the Cube of Rupture Velocity

<p>Source spectral models developed for strong ground motion simulations are phenomenological models that represent the average effect that the source processes have on near fault ground motion. Their parameters are directly regressed from the observations and often do not have clear meaning for the physics of the source process. We investigate the relation between the kinematic double-corner frequency (DCF) source spectral model JA19_2S (Ji and Archuleta, BSSA, 2020) and static fault geometry scaling relations proposed by Leonard (2010). We derive scaling relations for the low and high corner frequency in terms of static stress drop, dynamic stress drop, fault rupture velocity, fault aspect ratio, and relative hypocenter location. We find that the non-self-similar low corner frequency &#160;scaling relation of JA19_2S model for 5.3<<strong>M</strong><6.9 earthquakes is well explained using the fault length scaling relation of Leonard&#8217;s model combined with a constant rupture velocity. Earthquakes following both models have constant average static stress drop and constant average dynamic stress drop. The high frequency source radiation is controlled by seismic moment, static stress drop and dynamic stress drop but strongly modulated by the fault aspect ratio and the hypocenter&#8217;s relative location. The mean, scaled energy &#160;(or apparent stress) decreases with magnitude due to the magnitude dependence of the fault aspect ratio. Based on these two models, the commonly quoted average rupture velocity of 70-80% of shear wave speed implies predominantly unilateral rupture.</p>

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Variation of seismic scalar moment–corner frequency relationship during development of a hydraulic fracture system

The Leading Edge ◽

10.1190/tle38020123.1 ◽

2019 ◽

Vol 38 (2) ◽

pp. 123-129

Author(s):

Takashi Mizuno ◽

Joel Le Calvez ◽

Jim Rutledge

Keyword(s):

Hydraulic Fracture ◽

Stress Drop ◽

Static Stress ◽

Corner Frequency ◽

Fracture System ◽

Rupture Velocity ◽

Static Stress Drop ◽

Two Parameter ◽

Parameter Relation ◽

Scalar Moment

We propose to utilize the corner frequency and seismic scalar moment relation as a new approach to monitor temporal changes of static stress drop as well as rupture velocity during development of a hydraulic fracture system. We introduce a single parameter M1 to describe a two-parameter relation (scalar moment and corner frequency relation) and analyze temporal variation of this two-parameter relation. Because M1 relates rupture velocity and static stress drop, we can infer temporal variation of rupture velocity and stress drop quantitatively. The parameter M1 is calculated in two case studies. We document that two types of fracturing processes exist: (1) stable rupture velocity and static stress drop during the development of rupture and (2) increase of rupture velocity and/or static stress drop while the fracture system develops. In the latter case, one possible scenario is increase of permeability at each fracture plane during development of the fracture system.

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Microearthquakes and the nature of the creeping-to-locked transition of the San Andreas fault zone near San Juan Bautista, California

Bulletin of the Seismological Society of America ◽

10.1785/bssa0740010235 ◽

1984 ◽

Vol 74 (1) ◽

pp. 235-254

Author(s):

William H. Bakun ◽

Marcia McLaren

Keyword(s):

Fault Zone ◽

Stress Drop ◽

Seismic Moment ◽

Dynamic Stress ◽

San Andreas Fault ◽

Static Stress ◽

P Wave ◽

Apparent Stress ◽

San Andreas ◽

Static Stress Drop

Abstract Eighteen digital event recorders were deployed during May-June 1981 along the creeping-to-locked transition of the San Andreas fault zone near San Juan Bautista, California, as a supplement to the U.S. Geological Survey's central California seismic network. Analysis of 18 well-recorded microearthquakes (0.7 ≦ ML ≦ 2.8) located along the transition confirms the complexity of the crust and fault-zone structure of the transition region. Seismic-wave site amplification is 2 to 10 times greater at sites between the San Andreas and Sargent fault traces, consistent with other evidence for lower velocities in the upper 3 km of crust there. Routine mislocation of epicenters 2 to 4 km northeast of the Sargent fault are consistent with greater P-wave velocity northeast of the Sargent fault. Microearthquake source parameters are consistent with a more segmented and splayed fault geometry toward the northwest locked end of the transition. P-wave nodal planes for 10 microearthquakes located to the northwest, 9 on the Sargent fault, and 1 near the San Andreas, are oriented more westerly than nodal planes commonly obtained for the frequent moderate-size earthquakes on the creeping section of the San Andreas fault to the southeast. Static stress drop, dynamic stress drop, and apparent stress estimates all increase with seismic moment, with the apparent stress and dynamic stress drops equal to about 3 and 20 per cent, respectively of the static stress drop. Average fracture energies, calculated assuming complete stress drop, generally increase with source size (seismic moment, rupture area, seismic slip, etc.) from 7 to 3000 J/m2; the two events with anomalously low fracture energies occurred on the creeping section of the San Andreas fault.

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

Bulletin of the Seismological Society of America ◽

10.1785/bssa0740010027 ◽

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.

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

Seismological Research Letters ◽

10.1785/0220210098 ◽

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.

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