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The purpose of the study of Terrestrial Laser Scanner (TLS) application in an active volcanic crater is to detect the influence of gas emission and local atmospheric change into the accuracy of measurement. The measurement was conducted at Papandayan Volcano crater, along with the local temperature, humidity, and air pressure (thp). The measured target located near a gas emission hole gives a significant fluctuative range due to possible false return by gas particles. The refraction index was calculated using thp data. Two correction models were applied: velocitygeometry and atmospheric delay correction. The atmospheric delay correction gives a more reliable result, however their refraction index calculation does not accomodate specific volcanic gas yet. An intensity map obtained from TLS can also be used for rock segmentation. An experiment from some types of volcanic rocks shows that the intensity value is influenced by a weathering degree of rock outcrops. Rock segmentation using TLS intensity data for fresh outcrops is relatively easier, while for weathered rocks it still needs a field check for validation. The temperature of volcanic rocks also contributes to the intensity value. It is found that the intensity increases along with the temperature of rock. [ABSTRACT FROM AUTHOR]

The ability of radar to penetrate cloud is utilized to measure ground deformation related to volcanic activity of the tropical Ibu Volcano, Indonesia. Ground deformation in the vicinity of the volcano is believed to be related to subsurface magma activity. Besides cloud cover, the high density of vegetation, which is common in rainforests, is also a major obstacle for studying ground deformation in Indonesia. Therefore, a longer wavelength such as L-band radar data is suitable to address these problems. Using L-band differential interferometry it was found that there was an inflation-deflation region around the volcano, especially in the crater region before the eruption. [ABSTRACT FROM AUTHOR]

Along the Java trench the Australian-Oceanic plate is moving and pushing onto and subducting beneath the Java continental crust at a relative motion of about 70 mm/yr in NNE direction. This subduction-zone process imposed tectonic stresses on the fore-arc region offshore and on the land of Java, thus causing the formation of earthquake fault zones to accommodate the plate movement. Historically, several large earthquakes happened in Java, including West Java. This research use GPS surveys method to study the inter-seismic deformation of three active faults in West Java region (i.e. Cimandiri, Lembang and Baribis faults), and the co-seismic and post-seismic deformation related to the May 2006 Yogyakarta and the July 2006 South Java earthquakes. Based on GPS surveys results it was found that the area around Cimandiri, Lembang and Baribis fault zones have the horizontal displacements of about 1 to 2 cm/yr or less. Further research is however still needed to extract the real inter-seismic deformation of the faults from those GPS-derived displacements. GPS surveys have also estimated that the May 2006 Yogyakarta earthquake was caused by the sinistral movement of the (Opak) fault with horizontal co-seismic deformation that generally was less than 10 cm. The post-seismic horizontal deformation of the July 2006 South Java tsunami earthquake has also been estimated using GPS surveys data. In the first year after the earthquake (2006 to 2007), the post-seismic deformation is generally less than 5 cm; and it becomes generally less than 3 cm in the second year (2007 to 2008). [ABSTRACT FROM AUTHOR]

Land subsidence in the Bandung Basin has been historically detected and possibly caused by several factors, including groundwater withdrawal. It is presumed that land subsidence is still occurring, causing a wide-ranging impact on infrastructure and buildings. This study aimed to determine the current status of land subsidence in Bandung Basin by using the Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS). The source of Synthetic Aperture Radar (SAR) imagery used in this study is Sentinel-1 imagery from 2014 to 2021. Land subsidence was then estimated using the InSAR method and validated with the GPS results. Based on the interpretation of the InSAR results, the most significant land subsidence in the Bandung Basin occurred in the Gedebage and Dayeuhkolot districts. It is estimated that the average annual land subsidence for these districts is about 10 cm/yr, with a maximum amplitude of around 17 cm/yr. Considerable damages due to land subsidence were also found. InSAR-derived land subsidence showed a good agreement with the GPS-derived land subsidence. In conclusion, land subsidence has been confirmed by two independent methodologies in this region and tends to worsen in the Bandung Basin. [ABSTRACT FROM AUTHOR]

Hazardous tsunamis are known to be generated predominantly at subduction zones. However, the 2018 M w 7.5 Palu (Indonesia) earthquake on a strike-slip fault generated a tsunami that devastated the city of Palu. The mechanism by which this tsunami originated from such an earthquake is being debated. Here we present near-field ground motion (GPS) data confirming that the earthquake attained supershear speed, i.e. a rupture speed greater than the shear wave speed of the host medium. We subsequently study the effect of this supershear rupture on tsunami generation by coupling the ground motion to a 1-D non-linear shallow-water wave model accounting for both time-dependent bathymetric displacement and velocity. With the local bathymetric profile of Palu bay around a tidal station, our simulations reproduce the tsunami arrival and motions observed by CCTV cameras. We conclude that Mach (shock) fronts, generated by the supershear speed, interacted with the bathymetry and contributed to the tsunami. [ABSTRACT FROM AUTHOR]

We investigate three available coseismic fault models of the 2006 M7.8 Java tsunami earthquake, as reported by Fujii and Satake (2006), Bilek and Engdahl (2007), and Yagi and Fukahata (2011), in order to find the best coseismic model based on mechanisms of postseismic deformation associated with viscoelastic relaxation and afterslip. We construct a preliminary rheological model using vertical data, obtaining a final rheological model after we include horizontal and vertical components of afterslip in the further process. Our analysis indicates that the coseismic fault model of Fujii and Satake (2006) provides a better and more realistic result for a rheological model than the others. The best-fit rheological model calculated using the coseismic fault model of Fujii and Satake (2006) comprises a 60 ± 5 km elastic layer thickness with a viscosity of 2.0 ± 1.0 × 10 17 Pa s in the asthenosphere. Also, we find that afterslip is dominant over the horizontal displacements, while viscoelastic relaxation is dominant over the vertical displacement. Additionally, in comparison to the coseismic displacement found through GPS data taken at BAKO station, our calculation indicates that Fujii and Satake (2006) modeled coseismic displacements with less GPS data misfit than the other examined models. Finally, we emphasize that our methodology for evaluating the best coseismic fault model can satisfactorily explain the postseismic deformation of the 2006 Java tsunami earthquake. [ABSTRACT FROM AUTHOR]

Abstract: This study examines the factors of human activities causing environmental stresses on the subsurface environments in the urban settings of Jakarta. A major objective of this study is to identify the basin geometry and estimate how critical is the degradation of the subsurface environment within the basin, and it covered micro-palaeontology and chemical analyses, the decrease of water level, and GPS data. New data on shallow groundwater quality is provided and the results indicate strong evidence for human activities have influenced the degradation of the Jakarta subsurface environment. [Copyright &y& Elsevier]

In this work, land subsidence in Bandung Basin, Indonesia between 2002 and 2011 was mapped using the C-band ENVISAT ASAR and L-band ALOS PALSAR data. Twenty four ALOS PALSAR and thirty ENVISAT ASAR images acquired between 2002–2008 and 2007 – 2011, respectively, were analysed. Several locations that were experiencing land displacement were identified including Cimahi, Dayeuh Kolot, Rancaekek, Solokan Jeruk and Gedebage. The subsidence rates in the basin range from −240 mm/year to 40 mm/year. The comparison between the ALOS PALSAR and ENVISAT ASAR measurements, which showed good agreement, suggested the subsidence in many areas of the basin were steady between 2002 and 2011, except south Bandung. Acceleration of subsidence in south Bandung was observed between the measurements from the two datasets, likely as a result of increasing population and industries. The subsidence in the basin was expected mainly as a result of excessive groundwater extraction and soil consolidation caused by surficial loading. GPS survey data collected between 2002 and 2010 were used to validate the ALOS PALSAR and ENVISAT ASAR measurements. Good correlations were observed between InSAR and GPS measurements. The comparison between the land subsidence measurements and the groundwater level information showed there were some correlations between them. For every 1 m reduction in groundwater level per annum, ground subsidence of 20-23 mm per annum has been observed. The comparison results suggested that there was no evidence showing the aquifer in the basin is being recovered. [ABSTRACT FROM AUTHOR]

We present an interplate coupling model of the Australia-Java plate interface off the southwestern coast of Java, Indonesia, based on data from the Indonesian Permanent GPS Station Network from 2008 to 2010. The majority of vertical data indicate uplift, while the baseline change rate indicates coastal contraction in the middle of the network and coastal extension in the eastern part of the network. Using the rate of baseline length changes and the absolute rate of vertical displacements, we apply a geodetic inversion method by Yabuki and Matsu'ura (1992). From the inversion result, we interpret the main source of the observed velocity in West Java as resulting from contributions of (1) interplate coupling off Ujung Kulon-Pelabuhan Ratu at 20 to 40 km depth, with a slip rate range from 48 to 56 mm/yr, (2) interplate coupling off Pangandaran at 37 to 45 km depth with a slip rate of 48 to 55 mm/yr, (3) afterslip off Pangandaran within the rupture area of the 2006 M7.8 Java earthquake, in the depth range of 15-20 km, with a slip excess rate of 57-61 mm/yr. The absence of a megathrust earthquake for at least 300 years in this region implies seismic moment accumulation during this time period of 1.6x1021 Nm (~Mw 8.7) off Ujung Kulon-Pelabuhan Ratu, and 3.9x1021 Nm (~Mw 8.3) off Pangandaran, unless episodic slow slips release tectonic stress. [ABSTRACT FROM AUTHOR]

Highlights: [•] Afterslip and Maxwell viscoelastic relaxation explain deformation in northern Sumatra. [•] A rheological structure with elastic layer depth of 65±5km. [•] A rheological structure with Maxwell viscosity of 8.0±1×1018 Pas. [•] Our model is applicable to the GPS in northern Sumatra, Thailand, and Andaman–Nicobar. [ABSTRACT FROM AUTHOR]

Abstract: Jakarta is the capital of Indonesia. It is one of the largest cities with an around 10 million population as for 2010, covering an area of about 661 square kilometers. The land subsidence phenomena in several areas of Jakarta are well known for many years. Land subsidence does damage infrastructures in the city; therefore, it has to be closely monitored and analysed. In this paper, the authors have demonstrated the capability of the PALSAR sensor aboard the Japanese ALOS satellite for large-scale mapping of land subsidence in Jakarta. Mapping results were produced from 17 ALOS PALSAR L-band radar images using persistent scatterer radar interferometry (PSI). The GEOS-PSI software, developed by the Geodesy and Earth Observing Systems group at UNSW for PSI analysis, was used to detect and map those land subsidence. The results showed that the land in the area of Jakarta was deforming at different rates across several zones. The land subsidence measured from ALOS PALSAR imagery were cross-examined with the subsidence values obtained from 4 GPS campaign surveys by the authors at 19 stations between 2007 and 2010. The magnitudes and trends of the deformation obtained from both techniques agreed well in general for those pinpoints of GPS. After the removal of 2 suspected outliers in GPS measurements, the subsidence rate difference between the two techniques range from −29 to 6mm/year, with a standard deviation of 9mm/year and an average absolute difference of 8mm/year. This research has suggested that PSI with L-band ALOS PALSAR data can be a promising technique to complement the GPS surveying for monitoring land subsidence in super large cities like Jakarta. [Copyright &y& Elsevier]

Abstract: One of the most violent volcanic eruptions in recorded history is the Krakatau eruption on August 27, 1883. This caldera-forming eruption destroyed two thirds of the Krakatau volcanic island in the Sunda Strait resulting in the remaining three small islands later known as the Krakatau complex. From 1927 to 1929, eruptions in the center of Krakatau complex have produced a new volcano named Anak Krakatau, which continuously builds its body through eruptions until now. One eruption event took place between 2007 and 2008 with several eruptions that lasted in total from the end of October 2007 to August 2008. Eruptions were characterized by Strombolian activity with ash columns 1km high, as well as pyroclastic and lava flows. We monitored the ground deformation of Anak Krakatau Volcano by interfering PALSAR data from June 2007 to February 2009. The result of InSAR technique shows a complex pattern of ground deformation. Inflation up to 4cm, together with subsidence around the crater, was measured for almost three months before the eruption with a volume increase of approximately 1×106 m3. After the eruption, the southwest side of the volcanic cone subsided by 18cm, whereas the northeast side of the cone uplifted 12cm in almost two years. The observed ground deformation after the eruption can be explained by 4m of tensile opening along a dipping rectangular tensile dislocation buried in an elastic half-space, approximately 400m below sea level. [Copyright &y& Elsevier]

The global positioning system (GPS) can be utilised to detect ground deformations of the surface of a volcano. Ground deformation monitoring is considered one of the most effective tools for investigating the behaviour of active volcanoes. The decreasing cost of GPS hardware, together with the increased reliability of the technology, facilitates such demanding applications. GPS ground deformation measurements can be continuous, automatic, conducted in all weather conditions, and provide three-dimensional positioning results. Higher computing power also means that the complex mathematics required to process GPS baselines can be easily handled in near real time.During the past few years a methodology has been developed for processing data collected by GPS networks consisting of a mixed set of single-frequency and dual-frequency receivers. The strategy is to deploy a few permanent, ‘fiducial’ GPS stations with dual-frequency, geodetic-grade receivers surrounding an ‘inner’ network of low-cost, single-frequency GPS receivers. Such a configuration offers considerable flexibility and cost savings for geodynamic applications such as volcano deformation monitoring, which require a dense spatial coverage of GPS stations, and where it is not possible to establish permanent GPS networks using only expensive dual-frequency instrumentation.This configuration has recently been tested at the Mt. Papandayan volcano in West Java, Indonesia. The two-stage network design consists of an inner network of four single-frequency Canadian Marconi (CM) GPS receivers surrounded by three dual-frequency Leica CRS1000 GPS receivers. The inner network logged and transmitted GPS data from the ‘slave’ stations located on the volcano, to a base station. The combined processing of the CM and Leica receiver data was performed off-line so as to investigate the performance of such a mixed-mode system. The basis of the processing methodology is to separate the dual-frequency, ‘fiducial’ station data processing from the baseline processing involving the single-frequency receivers on the volcano. The data processing for the former was carried out using a modified version of the Bernese software, to generate a file of ‘corrections’ (analogous to Wide Area DGPS correction models for the distance dependent biases – primarily due to atmospheric refraction). These ‘corrections’ were then applied to the double-differenced phase observations from the inner receivers to improve the baseline accuracies. A description of the field testing (and its challenges) during February–March 2000, together with a discussion of some of the results are presented. [Copyright &y& Elsevier]