The temporal distribution of tremor activity exhibits a highly non-Poissonian behavior, and its maximum period clustering statistically describes the recurrence interval major bursts. Here, we examine variations in properties by assessing their characteristic times, which are determined distribution. By applying two-point correlation integral to some world's zones, including Shikoku, Kii-Tokai, Kyushu Japan; Cascadia, Jalisco, Guerrero Mexico; southern Chile; Taiwan; Manawatu New Zealand,...

Abstract Deep tectonic tremors have been observed together with signals in the very low frequency (VLF) band from 0.02 to 0.05 Hz, which identified as VLF events limited regions of subduction zones. By stacking broadband seismograms relative timing tremors, we detected similar all where occur western Japan. These are inverted obtain moment tensor, and fault‐normal slip vectors generally consistent geometry plate interface direction motion. Therefore, these probably radiated by shear on...

Abstract The sizes of deep tectonic tremors have never been accurately evaluated as a physical quantity. Here we estimate tremor size the band‐limited seismic energy rate at 2–8 Hz, with accurate evaluation path attenuation and site amplification waves in four subduction zones: Nankai, Cascadia, Jalisco, South Chile. size‐frequency statistics rate, which are characterized by median measure for each subregion, spatially variable. spatial variations categorized into three types, type...

Shallow slow earthquakes have been documented along shallow plate interfaces near trenches. Recent geophysical observation networks located offshore of Japan enable us to analyze tremors in the Nankai Trough and Trench. Onshore seismic stations are also important for detecting very low frequency (VLFEs) evaluating their seismicity prior deployment networks. This study analyzes data from ocean bottom seismometers estimate energy radiation such tremors, which we observe along-strike...

Abstract Fluid migration in subduction zones is a key controlling factor of slow and megathrust earthquakes at plate boundaries. During the migration, seismic velocity heterogeneous structures its pathways may be temporarily perturbed, preferably triggering earthquakes. Here, we show that transient changes heterogeneity occurred 0–9 months before shallow Nankai zone, Japan, using very long‐term (6–10 years) records ambient seafloor noise. The preceding to were observed near margin source...

SUMMARY The source characteristics of offshore seismic events, especially regular (or fast) and slow earthquakes, can provide key information on their physics frictional conditions at the plate boundary. Due to strong 3-D heterogeneities in regions, such as those relating sea water, accretionary prism small-scale velocity heterogeneity, conventional methods using a 1-D earth model may mis-estimate parameters duration radiation energy. Estimations could become severe inaccuracies for small...

Abstract We detected shallow very low frequency earthquakes (VLFEs) off the Cape Muroto and Kii Channel in Nankai subduction zone estimated their moment rate functions. Combining new previously catalogs, we obtained comprehensive catalog of VLFE functions along Trough. defined swarms investigated scaling relationships cumulative moments, activity area, durations each region. Detected were considered candidates for slow slip events. A similar relationship was observed between moments areas,...

Abstract Tectonic tremors in subduction zones, which result from slip at the deep plate interface, are known to exhibit a 12.4 h periodicity their activity, due tidal influence. Because stress can be calculated quantitatively, response of interface yield quantitative information about its frictional property. The relation between tremor rate and is investigated, an exponential widely confirmed, as observed by previous studies. This study particularly focuses on spatial variations...

Abstract Geological faults have frictional heterogeneity. Here we investigate the slip behavior of such heterogeneous in simplest situation, simulating antiplane shear along an infinite linear fault a 2‐D elastic model space, subjected to constant loading by external stresses characterized stiffness and plate‐motion velocity. The is discretized into many subfaults, each which has either velocity‐weakening (VW) or velocity‐strengthening (VS) friction law. We vary proportion that VW, revealing...

Abstract Deep and shallow slow earthquakes occur at the edge of seismogenic zone in Nankai subduction zone. under high‐temperature high‐pressure conditions, whereas lower temperatures pressures. Although these two types earthquake show qualitatively similar behaviors, such as deformation depleted high‐frequency seismic signals, their similarities have not yet been evaluated quantitative ways. In this work, we analyze tectonic tremors accompanied by very low frequency off Kii Peninsula,...

Abstract Slow earthquake size distributions have been found to follow either a power law or an exponential law, depending on the data set. We investigated distribution of shallow tectonic tremor events along Nankai trough, southwestern Japan, observed in 2009, 2015, 2016, and 2018 estimated seismic energy radiated during as measure event size. The obtained mostly followed with b value about 1, but also fits well largest events; this result indicates that follows Gutenberg‐Richter taper. If...

The COVID-19 pandemic that started at the end of 2019 forced populations around world to reduce social and economic activities; it is believed this can prevent spread disease. In paper, we report an analysis seismic noise during such induced activity reduction in Tokyo metropolitan area, Japan. Using data obtained from 18 stations Metropolitan Seismic Observation Network (MeSO-net), a two-step was observed timeline Tokyo. first occurred beginning March 2020 frequency band 20-40 Hz. This...

Abstract The mainshock‐aftershock sequence is one of the fundamental characteristics seismogenesis, yet physical mechanism aftershock generation remains poorly understood. simple explanation that aftershocks are caused by mainshock's redistribution strain energy not always applicable, especially for within mainshock slip area, where released. Here we show genesis can be modeled using a frictionally heterogeneous fault system. We conducted quasi‐dynamic numerical simulations rupture cycles on...

SUMMARY For a more quantitative discussion of slow earthquake activity, we evaluated the detectable limits very low frequency earthquakes (VLFEs), which are seismic observed in low-frequency (< 0.05 Hz) bands Nankai subduction zone. We performed numerical simulations using local 3-D model and used noise level permanent broad-band seismometers. First, investigated effects source-time functions on maximum amplitudes VLFE signals at certain station. The were controlled by moment rate....

Abstract Unlike tectonic tremors in subduction zones and along transform faults, the hosting structure for Taiwan remains debated. Tectonic have been discovered at ~30 km depth beneath southern Central Range, which is a young active collisional mountain belt. Here we provide first evidence focal mechanism of tremor using moment tensor inversion very low frequency band, employing broadband seismograms stacked relative to hypocentral time tremor. The best solution corresponds low‐angle thrust...

In the subduction zone south of Kyushu Island, at western extension Nankai zone, southwest Japan, age oceanic crust increases toward across subducting Kyushu-Palau ridge. While tremor activity is very high in Nankai, tectonic tremors have only recently been discovered Kyushu. this study, we examined beneath using an improved version envelope correlation method. doing so, distinguished from normal earthquakes and background noise criteria source duration spectrum ratio between low...

Precursory seismicity is often observed before a large earthquake. Small foreshocks occur within the mainshock rupture area, which cannot be explained by simple models that assume homogeneous friction on entire fault. In this study, we consider frictionally heterogeneous fault model, motivated recent observations of geologic faults and slow earthquakes. This study investigates slip behavior governed rate- state-dependent law. We finite linear consisting alternating velocity-weakening zones...

Abstract Tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground‐motion prediction and hazard mapping. Traditionally, recorded earthquakes magnitude ∼3–8 are develop equations; however, typical earthquake records may sparse in areas high hazard. In this study, we distance decay waves using measurements amplitude tectonic tremor, which is plentiful some regions. occurs frequency band interest (i.e., ∼2–8  Hz) located on...

Abstract The shallow accretionary prism of the Nankai Trough is a location where both large interplate earthquakes and slow occur. Since physical properties sedimentary materials are important topics for understanding structure prism, numerous ocean drilling expeditions have been conducted in that region to obtain logging data core samples. Although obtained samples normally measured onboard immediately after coring, estimations situ difficult because differences laboratory conditions....