Yousuke Miyagi

Surface deformation caused by shallow magmatic activity at Okmok volcano, Alaska, detected by GPS campaigns 2000-2002

Annual GPS campaigns were carried out at Okmok volcano in the Aleutian Islands, Alaska, between 2000 and 2002. Surface deformation detected by these measurements reveals that Okmok volcano has been inflating over these 3 years at a variable inflation rate. The horizontal displacements show a radial outward pattern, and there has been significant uplift of the caldera center. The uplift of the caldera center relative to the caldera rim was ∼2.1 cm during 2000–2001, and ∼6.7 cm during 2001–2002. The latter rate is quite consistent with that deduced from InSAR measurements spanning 1997–2000, but the deformation rate during 2000–2001 was much slower than during the preceding and succeeding periods. Shallow pressure source was inferred at a depth of ∼3.1 km beneath the approximate center of the caldera. The location of the source, ∼5 km laterally from the active vent, is consistent with that inferred from InSAR data during 1997–1998. The total increase in volume during 2000–2002 of the inferred source is ∼0.44 × 107m3, which is 3–8% of the amount of volume erupted in 1997. The GPS and InSAR data show that magma accumulation beneath Okmok was steady in rate and location during 1997–2002, except for a pause at some time between 2000 and 2001.

Crustal deformation associated with the 2011 Shinmoe-dake eruption as observed by tiltmeters and GPS

The National Research Institute for Earth Science and Disaster Prevention (NIED) developed volcano observation stations at the Kirishima volcanic group in 2010. The stations observed remarkable crustal deformation and seismic tremors associated with the Shinmoe-dake eruption in 2011. The major eruptive activity began with sub-Plinian eruptions (January 26) before changing to explosive eruptions and continuous lava effusion into the summit crater (from January 28). The observation data combined with GEONET data of GSI indicated a magma chamber located about 7 km to the northwest of Shinmoe-dake at about 10 km depth. The tiltmeter data also quantified detailed temporal volumetric changes of the magma chamber due to the continuous eruptions. The synchronized tilt changes with the eruptions clearly show that the erupted magma was supplied from the magma chamber; nevertheless, the stations did not detect clear precursory tilt changes and earthquakes showing ascent of magma from the magma chamber just before the major eruptions. The lack of clear precursors suggests that magma had been stored in a conduit connecting the crater and the magma chamber prior to the beginning of the sub-Plinian eruptions.

COSMO-SkyMed and ALOS-1/2 X and L band multi-frequency results in satellite disaster monitoring

In this paper we introduce recent results of studies performed under the cooperated activities between Japan Aerospace Exploration Agency (JAXA) and the Agenzia Spaziale Italiana (ASI) for disaster monitoring. Under this cooperation, we performed simulation study of coordinated observation by ALOS-2, COSMO-SkyMed and other SAR satellites in case of huge Nankai Trough Earthquake in Japan. The result proved that coordinated observation could improve observation frequency and reduce time to acquire seamless dataset over vast disaster areas. The COSMO-SkyMed PSInSAR study over Sakurajima in Japan revealed possible deformation caused by volcanic activities. We challenged flood detection case study by using both L band and X-band SAR images for developing semi-automatic discrimination of inundated areas in urban areas in northern Kyushu where were suffered by an unprecedented heavy rain in 2011. The comparative study to investigate the sensitivity of polarimetric parameters of L-band SAR and X band SARs shows the single image L band polarimetry provides effective information on landslides in mountainous area covered by vegetation.

Pressure Sources of the Miyakejima Volcano Estimated from Crustal Deformation Studies During 2011–2013

Following the eruption of the Miyakejima Volcano in the Izu Islands, Japan, in the year 2000, a continuous GPS network observed the ongoing contracting crustal deformation. Subsequently, a slight inflation of the island was detected from around 2006, and we initiated a campaign of dense GPS observations around the volcano from 2011. Precise crustal deformation studies indicated inflation in the southern part of the island and deflation around the center of the crater. Using these observations, we estimated that three magma sources (a shallow deflation sill under the crater, a southern inflation dyke, and a deep inflation spherical source) were activated during 2011–2013. In particular, the presence of an inflation dyke at an intermediate depth had not been inferred by previous studies. Accordingly, we posit that the supply of magma from a deep spherical source to the new dyke source has been initiated only recently.

Long-term lava extrusion after the 2011 Shinmoe-dake eruption detected by DInSAR observations

In January 2011, the latest eruption began at Shinmoe-dake volcano, Japan, and lava accumulated in the crater. Differential interferometric synthetic aperture radar (DInSAR) observations after the end of main eruption indicated continuous uplift on the lava surface. We estimated the volume increase of lava, and the volume change rate has decreased exponentially. Results from long-term DInSAR processing indicate slow subsidence outside the crater. We interpret that this subsidence is caused by deflation of a shallow source located beneath the crater, which is a reaction to the extrusion of lava. Between November 2011 and May 2013, the total volume of extruded lava within the crater is estimated to be 6.7 ± 0.1 × 104 m3, which is comparable to the deflation volume of the shallow source. The system is not closed within the shallow source to the crater; thus, long-term lava extrusion can be explained by continuous injection from a deeper source to the shallow source.

ALOS emergency observations by JAXA for monitoring earthquakes and volcanic eruptions in 2008

In 2008, many disasters occurred in different places around the world. Remote sensing technique contributed significantly to observing and monitoring those disasters that occurred in remote locations. The ALOS satellite has observed the entire world using three sensors since its launch, thus providing important results soon after disasters strike. By comparing optical images or SAR amplitude images acquired before and after the disaster, we can identify surface changes associated with earthquakes or volcanic eruptions. Such information helps us evaluate risks of second disasters. InSAR observation detected crustal deformation associated with earthquakes, and the geodetic information helped us to understand fault mechanisms.