Waveform Characteristics and Source Mechanisms of Deep Low-Frequency Earthquakes near Osorezan and Esan Volcanoes in Northern Japan

Sakoi, Hisayuki; Kosuga, Masahiro; Watanabe, Kazutoshi

doi:10.4294/zisin1948.54.3_397

Cited by 2 publications

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“…These seismic signals are deeper than the lowermost depth of other micro-earthquakes in the region. Clusters of these signals, in particular, located 15 km on August 24, 2013 gsabulletin.gsapubs.org Downloaded from southwest to the Esan volcanic complex, have been interpreted as attributable to magmatic infl ux into the magma chamber of the Esan volcanic complex (Sakoi et al, 2001).…”

Section: Tectonic and Magmatic Setting Of Esan Volcanic Complexmentioning

confidence: 99%

“…The internal pressure of the magma chamber at depth (P c ) connects with a magma pressure at the source (P s ), where the magma is assumed to be incompressible. As for pressure at the source (P s ), the depth of the deeper magma source can be assumed to be 20 km, because most LF seismic signals around the Esan volcanic complex occur below 20 km depth (Sakoi et al, 2001). In the model, the hydraulic connection between the source and the chamber is maintained at all times; thus, replenishment is enhanced (Pinel et al, 2010).…”

Section: Concept Of Magma Replenishment In the 2-d Elastic Modelmentioning

confidence: 99%

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Eruption history, conduit migration, and steady discharge of magma for the past 50,000 yr at Esan volcanic complex, northern Japan

Miura

Arai²,

Toshida

et al. 2013

Geological Society of America Bulletin

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We have undertaken a detailed field, petro logical, geochronological, and modeling study of Esan volcanic complex, northern Japan , in order to establish its eruptive history over the past 50,000 yr. The Esan volcanic complex includes seven lava domes, which are endogenous domes developed without basal edifi ces. Each dome was produced by intermediate to silicic magmas with 57-67 wt% SiO 2 that were erupted in magnitude 4-5 eruptions. Five explosively erupted pyroclastic units cover the aprons of these lava domes. The spatial and temporal relationships of the domes and the pyroclastic units have been determined in order to constrain the eruptive sequence of the Esan volcanic complex. A simple elastic model, assuming a hydraulic connection state, was utilized to study variations in long-term magma discharge at the Esan volcanic complex, which have been attributed to changes in magma storage conditions. The stepwise change in magma discharge with time, which is 4.2-5.3 × 10 4 m 3 /yr, is interpreted to refl ect a change between magma chamber radius (R c ) and magma depth (H c ) caused by an upward migration of magma. Assuming a continuous input of magma from a deep source at a constant supply rate, the magma storage system that existed during the early stage of the Esan volcanic complex has been renewed, which will result in a shorter recurrence interval between eruptions rather than a long period of dormancy (22,400 yr). Given this fi nding, and the fact that the most recent eruption occurred 9000 yr ago, there is currently a risk of a large eruption at the Esan volcanic complex.

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Section: Tectonic and Magmatic Setting Of Esan Volcanic Complexmentioning

confidence: 99%

Section: Concept Of Magma Replenishment In the 2-d Elastic Modelmentioning

confidence: 99%

Eruption history, conduit migration, and steady discharge of magma for the past 50,000 yr at Esan volcanic complex, northern Japan

Miura

Arai²,

Toshida

et al. 2013

Geological Society of America Bulletin

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Characteristics and generation mechanism of low-frequency earthquakes in the continental plate

Kosuga

2024

Jour. Geol. Soc. Japan

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Low-frequency earthquakes (LFEs) are anomalous earthquakes with a lower predominant frequency than that expected from the earthquake magnitude. LFEs are also unique with respect to their anomalously deep focal depths, where ordinary earthquakes do not occur. Due to these characteristics, the generation mechanisms of LFEs have attracted seismological, lithological, and geochemical attention. Here, we review the observation and their interpretation of LFEs. Most LFEs worldwide occur near active volcanoes, although some LFEs in Japan are detected far from such volcanoes on account of the high sensitivity of the seismic network. The focal mechanisms of LFEs include double-couple that represent fault slip, isotropic and compensated linear vector dipole (CLVD) that suggest a volume change in the source. Tomographic studies have shown that the source areas of LFEs are characterized by low velocity and high V P / V S ratios, suggesting the contribution of geofluids to LFE occurrence. Recent observations in Japan have revealed the occurrence of LFEs at shallow depths, even in the upper crust, sometimes located close to ordinary earthquakes. These observations and the variation in focal mechanisms support an LFEs source model of tensile-shear crack. LFEs can occur in the upper crust if the pore fluids are close to H 2 O rather than magma. The focal mechanism is double-couple if shear motion is dominant but is characterized by isotropic or CLVD components if crack opening is dominant, with the different focal mechanisms probably reflecting the pressure of pore fluids.

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Waveform Characteristics and Source Mechanisms of Deep Low-Frequency Earthquakes near Osorezan and Esan Volcanoes in Northern Japan

Cited by 2 publications

References 0 publications

Eruption history, conduit migration, and steady discharge of magma for the past 50,000 yr at Esan volcanic complex, northern Japan

Eruption history, conduit migration, and steady discharge of magma for the past 50,000 yr at Esan volcanic complex, northern Japan

Characteristics and generation mechanism of low-frequency earthquakes in the continental plate

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