Seismic Moment, Seismic Energy, and Source Duration of Slow Earthquakes: Application of Brownian slow earthquake model to three major subduction zones

Ide, Satoshi; Maury, Julie

doi:10.1002/2018gl077461

Cited by 35 publications

(48 citation statements)

References 44 publications

(82 reference statements)

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“…The BSE model is one candidate model seamlessly connecting observations across different frequency bands, but it may not provide an exact representation of real physical processes. While the BSE model presented here assumes a homogeneous Gaussian fluctuation, other types of randomness obeying power law distributions also provides essentially the same results at lower frequencies due to the central limit theorem and might better explain the impulsive nature of LFE signals (Ide & Maury, ). Such a non‐Gaussian distribution function may be more consistent with the spatial inhomogeneity or localization of the observed LFE and tremor sources (Chestler & Creager, ; Ohta & Ide, ; Rubin & Armbruster, ; Hawthorne & Bartlow, ) suggested that the BSE model is not completely consistent with very broadband observations.…”

Section: Resultsmentioning

confidence: 69%

“…Both the 1‐D and 2‐D models cover large time scales, ranging from subsecond to multiyear periods, to explain various slow earthquake characteristics, such as the proportionality of the seismic moment and event duration (Ide, Beroza, et al, ) above a certain threshold, the proportionality of the seismic energy and seismic moment (Ide et al, ), and an exponential distribution of observed tremor amplitudes (Watanabe et al, ). A 1‐D model has also been employed to characterize a variety of slow earthquake characteristics in different regions (Ide, ; Ide & Maury, ).…”

Section: Introductionmentioning

confidence: 99%

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Detection of Low‐Frequency Earthquakes in Broadband Random Time Sequences: Are They Independent Events?

Ide

2019

JGR Solid Earth

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Low‐frequency earthquakes (LFEs) are detected primarily from continuous seismograms using a matched‐filter technique with an impulsive template waveform in a relatively narrow frequency band. However, this method can also detect events from some kinds of random time sequences without clearly isolated events. Here this fact is demonstrated via simple numerical simulations using the synthetic moment accelerations from a model of broadband slow earthquake, the Brownian slow earthquake (BSE) model, and a totally random noise sequence. The matched‐filter technique identifies time sections including relatively isolated pulse‐like fluctuations, as signals in both time sequences, depending on the threshold. These waveforms, stacked relative to the signal timing, show a clear impulse similar to the assumed template in both time sequences, which highlights that we might potentially misinterpret an original time sequence as containing many isolated pulse‐like events. An important difference exists between the BSE model and random noise at frequencies much lower than the analyzed frequency band, with the stacked BSE sequence containing coherent signals at very low frequencies, which are not visible in the noise. Real observations in the Cascadia subduction zone also contain similar coherent signals at low frequencies, suggesting that these LFE signals are coincident with some slow slip. Therefore, so‐called LFEs might potentially be a misinterpretation due to signal processing, or at least they are the tip of the iceberg, with these signals forming a component of a very broadband slow‐earthquake‐like slip process that possibly occurs over sub‐second to multi‐year timescales.

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Section: Resultsmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

Detection of Low‐Frequency Earthquakes in Broadband Random Time Sequences: Are They Independent Events?

Ide

2019

JGR Solid Earth

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“…Ide (, ) and Ide and Maury () modeled complex variations in slow slip moment rate as the result of a slipping area that grows and shrinks over the course of the slow slip event. They predicted a random‐walk‐like frequency −2 decay for the moment rate power spectrum at high frequencies.…”

Section: Discussionmentioning

confidence: 80%

Observing and Modeling the Spectrum of a Slow Slip Event

Hawthorne

Bartlow

2018

JGR Solid Earth

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We estimate and model the normalized moment rate power spectrum of large slow slip events in Cascadia. We estimate the spectrum using data from GPS-derived slip inversions, borehole strain records, and beamforming-based tremor amplitudes. The normalized power spectrum initially decreases with frequency but then may flatten at periods of 1 to 10 days before decaying as frequency −n m at higher frequencies, where n m is between 1.1 and 1.4 when estimated from tremor and between 0.4 and 1.5 when estimated from strain. We explore one way to understand the observed spectrum: by modeling a month-long slow slip event as the sum of a steady background moment rate and a population of subevents. The subevents represent the wide variety of observed slow earthquakes, ranging from 0.5-s-long tremor to 3-hr-long rapid tremor reversals. We parameterize the subevents' magnitude distribution and moment-duration scaling, and we examine how the subevent population determines the slow slip spectrum. There are not enough data to rigorously test the subevent model, but we show that the data are consistent with a single continuum of slow earthquakes whose moments scale linearly with their duration, as has been proposed previously. Ide et al. (2007) proposed that all these bursts of slip, from LFEs to RTRs to large slow slip events, are components of a single slow earthquake family. Most well-observed slow earthquakes have roughly the same moment to duration ratio, or average moment rate (e.g., Ide et al. A Single Slow Earthquake Family, With One Moment-Duration Scaling?

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“… β controls the slope of the distribution; β = 2/3 b in the ordinary Gutenberg‐Richter law. Because the scaled energy of slow earthquakes is constant (Ide & Maury, ; Ide & Yabe, ; Yabe et al, ), we fit the TGR model to the tremor size distributions by replacing the seismic moment with the seismic energy according to the method described by Kagan (). By assuming M t = 3.0E4 J, we obtained corner energy values of 1.3E6, 9.0E6, 1.0E7, and 1.7E5 J for tremor activity in 2009, 2015, 2016, and 2018, respectively, and respective β values of 0.72, 1.0, 0.70, and 0.38.…”

Section: Discussionmentioning

confidence: 99%

“…Slow earthquakes have been classified according to their characteristic periods as impulsive low‐frequency earthquakes (LFEs) and low‐frequency tremor, with frequencies from 1 to 10 Hz; very low frequency earthquakes (VLFEs), with dominant periods of 10 to 100 s; and short‐term and long‐term slow‐slip events (SSEs), with durations from several days to a few years. Recently, these phenomena, which are considered to originate from the same fault slip, have been regarded as broadband slow earthquakes (Ide & Maury, ; Ide & Yabe, ; Ito et al, ).…”

Section: Introductionmentioning

confidence: 99%

Event Size Distribution of Shallow Tectonic Tremor in the Nankai Trough

Yabe

Sugioka

Shinohara

et al. 2019

Geophysical Research Letters

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Slow earthquake size distributions have been found to follow either a power law or an exponential law, depending on the data set. We investigated the size distribution of shallow tectonic tremor events along the Nankai trough, southwestern Japan, observed in 2009, 2015, 2016, and 2018 and estimated the seismic energy radiated during the events as a measure of event size. The obtained size distributions mostly followed a power law with a b value of about 1, but an exponential law also fits well the data of the largest events; this result indicates that the size distribution follows the Gutenberg‐Richter law with an exponential taper. If only the largest events were observed, an exponential size distribution would be obtained. This exponential taper could be attributed to a source fault limitation. Because the maximum event size differed among activity periods, the source fault size varied among them, although the source areas largely overlap.

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Seismic Moment, Seismic Energy, and Source Duration of Slow Earthquakes: Application of Brownian slow earthquake model to three major subduction zones

Cited by 35 publications

References 44 publications

Detection of Low‐Frequency Earthquakes in Broadband Random Time Sequences: Are They Independent Events?

Detection of Low‐Frequency Earthquakes in Broadband Random Time Sequences: Are They Independent Events?

Observing and Modeling the Spectrum of a Slow Slip Event

Event Size Distribution of Shallow Tectonic Tremor in the Nankai Trough

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