Tidal Stress/Strain and the b-values of Acoustic Emissions at the Underground Research Laboratory, Canada

Iwata, T.; Young, R. P.

doi:10.1007/s00024-005-2670-2

Cited by 7 publications

(4 citation statements)

References 23 publications

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“…The same explanation could apply to our observations since laboratory experiments previously showed that b value variations depend on stress normalized to the maximum failure strength [Scholz, 1968]. Our observed greater sensitivity is also consistent with observation of the b value of acoustic emissions in the laboratory varying with tidal stress [Iwata and Young, 2005].…”

Section: Resultssupporting

confidence: 92%

Axial Seamount: Periodic tidal loading reveals stress dependence of the earthquake size distribution (b value)

Tan

Waldhauser

Tolstoy

et al. 2019

Earth and Planetary Science Letters

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Key Points:• Above a threshold stress amplitude, b value decreases with increasing tidal stress.• b value varies by ∼0.09 per kPa change in Coulomb stress.• b values can be used to map small stress variations in the Earth's crust. AbstractEarthquake size-frequency distributions commonly follow a power law, with the b value often used to quantify the relative proportion of small and large events. Laboratory experiments have found that the b value of microfractures decreases with increasing stress. Studies have inferred that this relationship also holds for earthquakes based on observations of earthquake b values varying systematically with faulting style, depth, and for subduction zone earthquakes, plate age. However, these studies are limited by small sample sizes despite aggregating events over large regions, which precludes the ability to control for other variables that might also affect earthquake b values such as rock heterogeneity and fault roughness.Our natural experiment in a unique seafloor laboratory on Axial Seamount involves analyzing the size-frequency distribution of ∼60,000 microearthquakes which delineate a ring-fault system in a 25 km 3 block of crust that experiences periodic tidal loading of ±20 kPa. We find that above a threshold stress amplitude, b value is inversely correlated with tidal stress.The earthquake b value varies by ∼0.09 per kPa change in Coulomb stress. Our results support the potential use of b values to estimate small stress variations in the Earth's crust. IntroductionEarthquake occurrence is primarily controlled by the stress state on fault interfaces.Because in situ stress measurements are difficult to obtain, a proxy for estimating the stress state of fault zones through their seismic cycles is valuable for understanding earthquake occurrence and forecasting earthquakes. Earthquakes follow a power-law size-frequency distribution given as log 10 (N) = a − bM, where N is the number of earthquakes greater than or equal to magnitude M, and a and b are constants [Gutenberg and Richter, 1944]. The value a describes the total number of earthquakes while the b value describes the relative frequency of small and large magnitude earthquakes. In rock fracture experiments, acoustic emissions from small cracking events follow the same power-law size distribution [Scholz, 1968]. Furthermore, their b values have been found to decrease (larger proportion of large events) with increasing differential stress [Scholz, 1968;Amitrano, 2003;Goebel et al., 2013].The same stress dependence of b value has been inferred to apply to earthquakes. The b value of earthquakes has been found to vary systematically with faulting style , depth [Spada et al., 2013], and for subduction zone earthquakes, plate age [Nishikawa and Ide, 2014]. These observations are consistent with the earthquake b value decreasing with increasing differential stress [Scholz, 2015]. However, these studies were re--2-

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Section: Resultssupporting

confidence: 92%

Axial Seamount: Periodic tidal loading reveals stress dependence of the earthquake size distribution (b value)

Tan

Waldhauser

Tolstoy

et al. 2019

Earth and Planetary Science Letters

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“…Because the b-value (or β) may have a temporal and/or regional (lateral and vertical) variation (e.g. Ogata & Katsura 1993;Mori & Abercrombie 1997;Schorlemmer et al 2004;Iwata & Young 2005), one might doubt the validity of our statistical model where we incorporate the GR law with a single b-value. However, the influence of such variations is not noticeable in Fig.…”

Section: O D E L L I N G T H E D E T E C T I O N C a Pa B I L I T Ymentioning

confidence: 99%

Low detection capability of global earthquakes after the occurrence of large earthquakes: investigation of the Harvard CMT catalogue

Iwata¹

2008

Geophysical Journal International

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SUMMARY We investigated the detection capability of global earthquakes immediately after the occurrence of a large earthquake. We stacked global earthquake sequences after occurrences of large earthquakes obtained from the Harvard centroid‐moment tensor catalogue, and applied a statistical model that represents an observed magnitude–frequency distribution of earthquakes to the stacked sequence. The temporal variation in model parameters, which corresponds to the detection capability of earthquakes, was estimated using a Bayesian approach. We found that the detection capability of global earthquakes is lower than normal for several hours after the occurrence of large earthquakes; for instance, the duration of lowered detection capability of global earthquakes after the occurrence of an earthquake with a magnitude of seven or larger is estimated to be approximately 12 hr.

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“…For example, Hartzell & Heaton (1989) searched for a fortnightly tidal periodicity in the Southern California and global earthquake catalogue, however, no such periodicity was observed. On the other hand, Iwata (2002) and Iwata & Young (2005) demonstrated that fluctuations of tidal stresses at times of full/new moon correlate with increased activity of acoustic emissions. The b-values of acoustic emissions were found to be significantly higher just after the times of full/new moon suggesting that b-values become larger during periods of high stresses.…”

Section: Introductionmentioning

confidence: 99%

Tidal stress triggering of earthquakes in Southern California

Bucholc

Steacy

2016

Geophys. J. Int.

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We analyse the influence of the solid Earth tides and ocean loading on the occurrence time of Southern California earthquakes. For each earthquake, we calculate tidal Coulomb failure stress and stress rate on a fault plane that is assumed to be controlled by the orientation of the adjacent fault. To reduce bias when selecting data for testing the tide-earthquake relationship, we create four earthquake catalogues containing events within 1, 1.5, 2.5 and 5 km of nearest faults. We investigate the difference in seismicity rates at times of positive and negative tidal stresses/stress rates given three different cases. We consider seismicity rates during times of positive versus negative stress and stress rate, as well as 2 and 3 hr surrounding the local tidal stress extremes. We find that tidal influence on earthquake occurrence is found to be statistically non-random only in close proximity to tidal extremes meaning that magnitude of tidal stress plays an important role in tidal triggering. A non-random tidal signal is observed for the reverse events. Along with a significant increase in earthquake rates around tidal Coulomb stress maxima, the strength of tidal correlation is found to be closely related to the amplitude of the peak tidal Coulomb stress (τ p). The most effective tidal triggering is found for τ p ≥ 1 kPa, which is much smaller than thresholds suggested for static and dynamic triggering of aftershocks.

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Tidal Stress/Strain and the b-values of Acoustic Emissions at the Underground Research Laboratory, Canada

Cited by 7 publications

References 23 publications

Axial Seamount: Periodic tidal loading reveals stress dependence of the earthquake size distribution (b value)

Axial Seamount: Periodic tidal loading reveals stress dependence of the earthquake size distribution (b value)

Low detection capability of global earthquakes after the occurrence of large earthquakes: investigation of the Harvard CMT catalogue

Tidal stress triggering of earthquakes in Southern California

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