Origin of transient self‐potential signals associated with very long period seismic pulses observed during the 2000 activity of Miyakejima volcano

Abstract

Origin of the previously reported transient geoelectrical (self-potential, SP) signals in the Miyakejima 2000 activity, that repeatedly occurred concurrently with very long period (VLP) seismic pulses, was investigated. SP waveforms stacked across repeated VLP events showed a step-like rise followed by a gradual decay at all stations spread over the island of 8 km diameter. Within a realistic range of hydrological diffusivity, the short time constants of the SP signals cannot be explained by the electrokinetic effect caused by fluid flow within a limited volume, proposed earlier as a fluid injection hypothesis. On the other hand, poroelasticity predicts an island-wide distributed flow field to occur almost instantaneously upon VLP events due to the step of strain field imposed by the mechanical event. We propose that the observed SP signals resulted from the streaming current by this island-wide flow field. Our quantitative model, assuming a vertical tensile crack as a mechanical source, which has been suggested by preceding seismic studies, can explain the time constants and the amplitude of the SP signals (both spatial pattern and absolute amplitude), within a reasonable range of rock properties and the scalar moment of the mechanical source (VLP event). Location and attitude of the mechanical source were well constrained by grid search and are consistent with those estimated earlier from other types of data.

Mechanisms of step‐like tilt changes and very long period seismic signals during the 2000 Miyakejima eruption: Insights from kinematic GPS

“…Kumagai et al [2001] noted that moment tensors for the TC/VLP events were dominated by volumetric change components; therefore, volumetric sources were suggested as the most likely forward model. Several models have been proposed in previous studies: a tensile vertical crack [Kumagai et al, 2001;Kuwano et al, 2015], a sill [Fujita et al, 2002[Fujita et al, , 2004, and an ellipsoidal column [Kobayashi et al, 2012]. In this study, we considered a tensile crack [Okada, 1985], a finite spherical pressure source [McTigue, 1987], an arbitrarily oriented spheroidal cavity [Cervelli, 2013], and an ellipsoidal cavity [Davis, 1986], which together can approximately represent all of the proposed models.…”

Self‐Potential Ambient Noise and Spectral Relationship With Urbanization, Seismicity, and Strain Rate Revealed via the Taiwan Geoelectric Monitoring Network

“…The SP signals occur in nature when electrolytes with different concentrations of ions come into galvanic contact with each other or where groundwater flows go through a capillary or a porous medium due to a hydraulic gradient (Revil & Jardani, 2013). In recent decades, the SP method has been becoming an important component in geophysical surveys on the areas of groundwater flow (Jardani et al, 2006;Mao et al, 2015;Sill, 1983), dam seepage monitoring (Al-Saigh et al, 1994;Ikard et al, 2014;Panthulu et al, 2001), volcanic monitoring (Aizawa et al, 2005;Corwin & Hoover, 1979;Kuwano et al, 2015), and earthquake precursor (Chen & Chen, 2016;Chen et al, 2017;Corwin & Morrison, 1977;Ramirez-Rojas et al, 2004). However, the SP signals are sensitive to anthropogenic factors, such as electric trains, factories, and power pipelines (Fraser-Smith & Coates, 1978;Harada et al, 2004;Ishikawa et al, 2007;Oettinger et al, 2001;Saito et al, 2011;Takahashi et al, 2007;Viljanen & Pirjola, 1994), and to natural factors, such as solar-terrestrial interactions, groundwater flows, and ocean tides (Fujii et al, 1995;Huang & Liu, 2006;Jardani et al, 2006;Lanzerotti et al, 2000).…”

Hydrothermal and Magmatic System of a Volcanic Island Inferred From Magnetotellurics, Seismicity, Self‐potential, and Thermal Image: An Example of Miyakejima (Japan)

“…(b) Locations of magnetotelluric stations (black triangles), broadband seismometers (black hexagons), and self-potential measurements (blue points), (c) Simplified geological map overlain with topography showing the three main volcanic activity periods, together with fumaroles and springs (red and purple points, respectively). Colored stars indicate mechanical sources and depth associated to the shallow magmatic chamber inferred by several studies: Kuwano et al [2015] from transient self-potential signal, Nishimura et al [2002] from GPS data, Kobayashi et al [2012] from velocity waveforms inversion using verylong-period events, Kumagai et al [2001] and Kikuchi et al [2001] from very long period seismic pulse. Maps were created using Esri ArcGIS 10.3 software (http://www.esri.com) with free digital elevation models: upper panel used the ASTER GDEM land model (https://asterweb.jpl.nasa.gov/gdem.asp) and the GEBCO bathymetry model (https://download.gebco.net/); bottom panels topography was obtained with the 5-m resolution digital elevation model of Miyakejima from the Geospatial Information Authority of Japan (https://www.gsi.go.jp/kiban).…”

“…Colored stars indicate mechanical sources and depth associated to the shallow magmatic chamber inferred by several studies: Kuwano et al. [2015] from transient self‐potential signal, Nishimura et al. [2002] from GPS data, Kobayashi et al.…”