Tracking the North Korean nuclear explosion of 2006, using seismic data from Japan and satellite data from Taiwan

The location of the 2006 nuclear explosion in North Korea has been accurately imaged by back-projected regional Pn waves recorded by the Japanese Hi-net array. Based on the determined location, the nuclear explosion site can be identified from geo-referenced FORMOSAT-2 satellite images. The seismically determined epicenter is about 2.5 km northeast of the original estimate of its absolute location. Results indicate that a remote suspect event had been unambiguously detected and accurately located by a dense array within a regional distance. Employing ground truth correction, the satellite images can be referenced for shifting the array-determined epicenter to its absolute position. After correction, this event can be treated as a reference event for accurately locating future nuclear explosions. Our study utilizes public information from a dense seismic network and further demonstrates that commercial observation satellites can accurately monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty, as well as earthquake and tsunami hazards almost in real time.     

Multiphase flow above explosion sites in debris-filled volcanic vents: Insights from analogue experiments

Discrete explosive bursts are known from many volcanic eruptions. In maar–diatreme eruptions, they have occurred in debris-filled volcanic vents when magma interacted with groundwater, implying that material mobilized by such explosions passed through the overlying and enclosing debris to reach the surface. Although other studies have addressed the form and characteristics of craters formed by discrete explosions in unconsolidated material, no details are available regarding the structure of the disturbed debris between the explosion site and the surface. Field studies of diatreme deposits reveal cross-cutting, steep-sided zones of non-bedded volcaniclastic material that have been inferred to result from sedimentation of material transported by “debris jets” driven by explosions. In order to determine the general processes and deposit geometry resulting from discrete, explosive injections of entrained particles through a particulate host, we ran a series of analogue experiments. Specific volumes of compressed (0.5–2.5 MPa) air were released in bursts that drove gas-particle dispersions through a granular host. The air expanded into and entrained coloured particles in a small crucible before moving upward into the host (white particles). Each burst drove into the host an expanding cavity containing air and coloured particles. Total duration of each run, recorded with high-speed video, was approximately 0.5–1 s. The coloured beads sedimented into the transient cavity. This same behaviour was observed even in runs where there was no breaching of the surface, and no coloured beads ejected. A steep-sided body of coloured beads was left that is similar to the cross-cutting pipes observed in deposits filling real volcanic vents, in which cavity collapse can result not only from gas escape through a granular host as in the experiments, but also through condensation of water vapour. A key conclusion from these experiments is that the geometry of cross-cutting volcaniclastic deposits in volcanic vents is not directly informative of the geometry of the “intrusions” that formed them. An additional conclusion is that complex structures can form quickly from discrete events.     

Mechanism of explosive eruption revealed by geophysical observations at the Sakurajima,Suwanosejima and Semeru volcanoes

A common sequence of phenomena associated with volcanic explosions is extracted based on seismic and ground deformation observations at 3 active volcanoes in Japan and Indonesia. Macroscopic inflation-related ground deformations are detected prior to individual explosions, while deflations are observed during eruptions. Precursory inflation occurs 5 min to several hours before eruption at the Sakurajima volcano, but just 1–2 min at Suwanosejima and 3–30 min at the Semeru volcano. The sequence commences with minor contraction, which is detected by extensometers 1.5 min before eruption at Sakurajima, as a dilatant first motion of the explosion earthquakes 0.2–0.3 s before surface explosions at Suwanosejima, and as downward tilt 4–5 s prior to eruption at the Semeru volcano. The sequence is detected for explosive eruptions with > 0.1 μrad tilt change at Sakurajima, 90% at Suwanosejima and 75% at Semeru volcanoes. It is inferred that the minor contraction is caused by a volume and pressure decrease due to the release of gas from a pocket at the top of the conduit as the gas pressure exceeds the strength of the confining plug. The subsequent violent expansion may be triggered by sudden outgassing of the water-saturated magma induced by the decrease in confining pressure.     

4D velocity of Strombolian eruptions and man-made explosions derived from multiple Doppler radar instruments

We used a novel system of three continuous wave Doppler radars to successfully record the directivity of i) Strombolian explosions from the active lava lake of Erebus volcano, Antarctica, ii) eruptions at Stromboli volcano, Italy, and iii) a man-made explosion in a quarry.     

Characterization of low-temperature pyroclastic surges that occurred in the northeastern Japan arc during the late 19th century

Three eruption events occurring in the central part of the northeastern Japan arc were investigated and compared: Adatara AD1900, Zao AD1895, and Bandai AD1888. Producing low-temperature (LT) pyroclastic surges, these events are characterized by steam eruptions ejecting no juvenile material. These eruptions' well-preserved eruptive deposits and facies facilitated granulometric analyses of the beds, which revealed the transport and deposition mechanisms of LT surges. Combining these results with those of investigations of documents reporting the events, we correlated each eruption to the relevant individual bed and reconstructed the LT surge development sequence. Important findings related to the transport and deposition modes are the following. (1) Bed sets consisting of thin, laminated ash and its overlying thick massive tuff were recognized in the Adatara 1900 proximal deposits. The bed set was probably produced by a strong wind that discharged and propagated quickly from the vent (leading wind) and a gravitationally segregated, highly concentrated flow originated from the eruption column, within a discrete eruption episode. A similar combination might have occurred during the first surge of the Bandai 1888 event. (2) Comparison of the proximal and distal facies for the largest eruption of Adatara 1900 event indicates that the initial turbulence of the eruption cloud decreased rapidly, transforming into a density-stratified surge with a highly concentrated part near the base. Similar surges occurred in the climatic stage of Zao 1895. (3) Bandai 1888 ejecta indicate massive beds deposited preferentially at topographic lows. Co-occurring planar beds showed no topographic affection, as indicated by the topographic blocking of a stratified surge. The observed facies–massive tuffs, crudely stratified tuffs, and thin bedded tuffs–are compatible with those for high-temperature surges. At Bandai, absence of dune bedded tuffs and commonly poorer sorting in the LT surge deposits might be attributable to poor thermally induced turbulence of eruption columns. Condensation of vapor in the surges might have contributed to the poor sorting. The estimated explosion energies were 6 × 10¹³ J for Adatara AD1900, 6.5 × 10¹⁰ J for Zao AD1895, and 6.5 × 10¹⁵ J for Bandai AD1888, implying that the three events were hydrothermal eruptions with distinctive eruptive mechanisms. Regarding eruption sources, the Adatara 1900 event was caused solely by thermal energy of the hydrothermal fluid, although magma intrusion likely triggered evolution of hydrothermal systems at Zao in 1895. Steam eruptions in the Bandai 1888 event occurred simultaneously with sudden exposure of the hydrothermal system, whose triggers require no internal energy.     

Control Experiments for Underwater Cultural Relics Survey by Marine Geophysical of Acoustics

Marine geophysical acoustic methods are a powerful tool for high-precision, large-scale underwater archaeological relics investigations and research in the shallow water. There is a complex coupling relationship between the marine environment and the preservation of underwater cultural relics, which leads to great uncertainty based on the detection data to deduce the existence and distribution of underwater cultural relics. In the past 30 years, the controllable experiments of acoustic methods for underwater cultural relics show that different side-scan sonar systems have varied acoustic response. Multi-beam sonar can be used to study the temporal variation of underwater cultural relics, while shipwreck partially or totally embedded in seabed sediments can be detected by sub-bottom profile. The control experiment will increase the understanding of the acoustic response for different underwater cultural types. Control experiment on the underwater cultural relics can provide a reference for the correlation between detection results and interpretation accuracy, and hopefully provide a systematic solution for underwater cultural survey in an efficient way and on a wide-scale, thus better protecting and managing underwater cultural relics.     

A critique of the UK’s JNCC seismic survey guidelines for minimising acoustic disturbance to marine mammals: Best practise?

The United Kingdom’s statutory conservation agency, the Joint Nature Conservation Committee (JNCC), developed guidelines in 1995 to minimise acoustic disturbance of marine mammals by oil and gas industry seismic surveys. These were the first national guidelines to be developed and have subsequently become the standard, or basis, of international mitigation measures for noise pollution during seismic surveys. However, relatively few aspects of these measures have a firm scientific basis or proven efficacy. Existing guidelines do not offer adequate protection to marine mammals, given the complex propagation of airgun pulses; the difficulty of monitoring in particular the smaller, cryptic, and/or deep-diving species, such as beaked whales and porpoises; limitations in monitoring requirements; lack of baseline data; and other biological and acoustical complications or unknowns. Current guidelines offer a ‘common sense’ approach to noise mitigation, but in light of recent research and ongoing concerns, they should be updated, with broader measures needed to ensure adequate species protection and to address data gaps.     

爆破与地震的拐角频率比较

应用辽宁地震台网记录的爆破与地震数字资料,采用小波计算方法,对该区域记录的爆破与地震计算S波拐角频率,将计算结果与前期采用PITSA软件得到的结果进行比较,试图获得爆破与地震识别的定量指标。     

天然地震与人工爆破的波形小波特征研究div

研究了如何从天然地震和人工爆破事件的波形记录中提取出有效、适用的波形特征,以用于对爆破事件的识别．首先对波形记录进行了4层小波包变换;然后对变换得到的最后一层小波包系数提取3种波形特征:能量比特征、香农熵特征及对数能量熵特征;最后利用upsilon;-SVC支持向量分类机对这3种特征的分类能力进行了外推检验．通过选用不同地区、不同台站、不同震级的天然地震与人工爆破的波形记录,力求提取的特征量能尽可能地反映天然地震与人工爆破波形的本质区别,尽量弱化震中距、震级等因素对识别效果的影响．结果表明,上述３种特征中以香农熵特征的识别效果最好,能反映天然地震与人工爆破的本质区别,可作为识别天然地震与人工爆破的一个有效判据．      

The spatial structure of local surficial sediment characteristics on Georges Bank,USA

Georges Bank is one of the world’s most productive marine ecosystems, but the lack of accurate broad-scale sediment maps presently limits habitat assessments and spatial fisheries management. From 1999 to 2009 we surveyed 36,669 km² of Georges Bank using 2.8 and 0.6 m² quadrats viewed with live underwater video (video quadrats). The sediment types observed in 61,604 quadrats were used to map and evaluate spatial structure of local surficial sediment coarseness, dominance, heterogeneity, and maximum size characteristics at a 1 km² spatial resolution. Sand dominated sediment covered 62% of the study area, and there was a logarithmic decline in coverage by larger, coarser and more heterogeneous sediments. Gravel dominated sediments covered 38% of the study area and were more than twice as abundant as previously estimated. A 12,890 km² swath of gravel dominated seabed stretched from Cape Cod to northeastern Georges Bank consistent with estimates of prehistoric glacial extent. Within the swath there were 14 large gravel outcrops (15–2743 km²) . This work increases the spatial resolution of sediment information available for habitat assessments and spatial fisheries management on Georges Bank by two orders of magnitude. The four sediment characteristics we evaluated support further detailed investigations of the Bank’s benthos, including the influences of surficial sediment characteristics on species and community distributions, and more spatially accurate estimates of seabed roughness. Finally, this work demonstrates the use of video quadrats as an alternative to traditional grab sampling and modern acoustic sampling for continental shelf-scale mapping.