No description available.

No description available.

No description available.

No description available.

No description available.

Although there is no obvious reason why seismic 6-value and the spatial fractal dimension of earthquakes, D, should be related, there are several reports of observed empirical correlations between these two quantities. In order to investigate this phenomenon, and attempt to relate it to different types of earthquakes, industrially induced seismicity in The Geysers geothermal area, California and earthquake swarms in Long Valley caldera, California were analysed. Raw seismograms from the Unocal-NEC-Thermal network in The Geysers were processed automatically, calculating magnitudes from coda lengths and locating them using a three-dimensional velocity model. Seismicity correlated with the locations of commercial wells and surface fault locations. The entire Geysers dataset was too complex for clear correlations between b, D, seismicity and injection to be observed. In several cases, short pulses of injection induced bursts of seismicity of either small-magnitude, clustered events or large-magnitude diffuse seismicity, resulting always in a transient anomaly of negative b/D. However, sometimes pulses of injection were not accompanied by b/D transients and sometimes b/D transients were not accompanied by known injection. The latter cases may or may not indicate undisclosed injection activity. A seismic crisis in Long Valley caldera was associated with major b/D anomalies that accompanied migration of the activity from a hydrothermal zone on the south edge of the resurgent dome to the right-lateral, blind, near-vertical South Moat fault to the immediate south. The results indicated that the hydrothermal zone is an inhomogeneous structure whereas the South Moat has a mature, coherent fault plane, capable of generating magnitude M = 6 earthquakes and posing a threat to the town of Mammoth Lakes.

Volcanic rocks which outcrop over 40 sq. km in eastern Jersey and which have a maximum thickness of 25 km have been mapped in detail. Basaltic and andesitic lavas, tuffs and agglomerates, which have been affected by keratophyric alteration, are overlain by numerous ignimbrite cooling units, the youngest of which are generally aphyric, the oldest being porphyritic. Local rhyolites, tuf'fs and andesites occur among the igniinbrites. The volcanics are essentially conformable upon Brioverian sediments and are regarded as being late Precambrian in age. Cadomian E-W and N-B fold phases, with associated faulting, are largely responsible for the present outcrop pattern. The petrology and geochemistry of these volcanics have been studied. Together with the regional distribution of similar late Precambrian volcanism they indicate that the caic-alkaline suite was generated soon after the initiation of the global tectonic movements which eventually produced the Caledonides. The basalts and andesites are thought to result from the partial melting of a descending lithospheric plate within the mantle, the magmas thus produced being modified en route to the surface by fractionation and crustal contamination under a variable The rhyolitic maginas were produced by crustal anatexis and collected in high-level magma chambers prior to their eruption. Post.-orogenic Cadomian plutonics which invade the volcanics are also caic-alkaline but are chemically distinct from the extrusives. The petrology and geochemistry of a dyke swarm which invades the volcanics and just postdates emplacement of the plutonics is also discussed. This appears genetically related to the plutonic complexes and was generated close to the base of the crust.

No description available.

Volcanoes are dynamic evolving structures, with life cycles that are punctuated by episodes of flank instability. Putauaki (Mount Edgecumbe) is a stratovolcano located onshore in the Bay of Plenty, New Zealand. The aim of this study was to assess the stability of Putauaki and analyse the risk associated with volcanic collapse. To achieve this objective, a multidisciplinary approach was used, incorporating geomorphological and geological mapping, rock mass classification, laboratory testing to identify geotechnical properties of materials representative of the volcano, stability modelling, and analysis of landslide run-out zones. Putauaki comprises two predominant features including the larger and younger Main Cone (the summit lying 820 m a.s.l., slope angles up to 36 ), and smaller and older Main Dome (the summit lying 420 m a.s.l., slope angle of 24 ). Both features show little evidence of erosion or surface water. Rock mass description defined six lithotechnical units including indurated andesite, indurated dacite, scoriaceous andesite, altered andesite (all categorised as hard rocks), and block and ash flow and Matahina Ignimbrite (both categorised as soft rocks). The uniaxial compressive strength (UCS) of indurated andesite and indurated dacite was 60 4 MPa and 44.7 0.9 MPa respectively, correlating with moderately strong rock. Discontinuities of the indurated units were widely spaced, showed medium persistence and wide aperture, and were slightly weathered. Infill comprised predominantly loosely packed, very strong, coarse gravel. UCS of scoriaceous andesite and altered andesite was 25 5 MPa and 15 1 MPa respectively, allowing categorisation as very weak rock. Discontinuities of scoriaceous andesite were widely spaced, showed high persistence and wide aperture, and were moderately weathered. Discontinuities of the altered andesite were moderately spaced, showed low persistence and wide aperture, and were highly weathered. Infill of scoriaceous and altered andesite was loosely packed, moist, weak to very weak medium gravel. The block and ash flow was a poorly sorted, loosely packed, sandy, gravely and cobble rich matrix supported deposit. The Matahina Ignimbrite was a very weak, discontinuity-poor deposit. Shear box testing indicated cohesion and friction angle of 0 MPa and 42.1 (block and ash flow) and 1.4 x 10-3 MPa and 41.7 (Matahina Ignimbrite) respectively. These values are similar to published values. Correlation of each lithotechnical unit to its respective rock mass description site allowed approximate boundaries of each unit to be mapped. Each unit's mass strength was combined with measured bulk densities and incorporated into two dimensional slope profiles using the stability modelling package GalenaTM. Ten slope profiles of Putauaki were constructed. Failure surfaces for each slope profile were defined using the Bishop simplified multiple analysis method. Four slope profiles showed the potential for small scale failure (less than 0.1 km2 of material). The remaining six slope profiles showed the potential for large scale failure (greater than 0.1 km2 of material). Stability of these six slope profiles was investigated further in relation to earthquake force, watertable elevation, and a disturbance factor of the rock mass (D). Conditions of failure graphs for profile 6a showed that at low D (less than 0.4), earthquake forces and watertable elevation must be unrealistically high for the region (greater than 0.33 g; greater than 15% watertable elevation) in order produce a factor of safety less than 1. The remaining five slope profiles showed potential to be unstable under realistic earthquake forces and watertable elevations. Two of these profiles were unable to achieve stability at D greater than 0.8 (profile 4) and D greater than 0.9 (profile 5). A D value of 0.6 (intermediate between 0.4 and 0.8) is argued to most realistically represent Putauaki. The fact that Putauaki has not undergone large scale failure to date supports the conclusion that the constructed models overestimate the influence of those factors which promote slope instability. Maximum and minimum landslide run-out zones were constructed for the slope profiles exhibiting the potential for large scale failure. Definition of the position and extent of maximum and minimum run-out zones assumed H/L (fall height to run-out length) ratios of 0.09 and 0.18 respectively, as well as the 'credible flow path' concept. Identified impacts of landslides sourced from Putauaki include inundation of Kawerau Township, Tarawera River, forestry operations, road networks, and power supplies. Based on these impacts, the risk posed by landslides from each slope profile was categorised as ranging from relatively low to relatively high. Landslides sourced from the south-west flanks pose a relatively low risk due to their prerequisite of unrealistically high watertable elevations and earthquake forces. Landslides sourced from the north-west flanks pose a relatively high risk as minimum run-out will inundate north-east parts of Kawerau Township. Landslides sourced from the eastern flanks pose a moderate risk due to their run-out zones avoiding Kawerau Township.

Ground deformation due to volcanic magma intrusion is recognised as an important precursor of eruptive activity at a volcano. The Global Positioning System (GPS) is ideally suited for this application by being able to measure three-dimensional coordinate changes of the monitoring points over time. Due to the highly disturbed ionosphere in equatorial regions, particularly during times of maximum solar activity, a deformation monitoring network consisting entirely of single-frequency GPS receivers cannot deliver baseline solutions at the desired accuracy level. In this thesis, a mixed-mode GPS network approach is proposed in order to optimise the existing continuous single-frequency deformation monitoring system on the Papandayan volcano in West Java, Indonesia. A sparse network of dual-frequency GPS receivers surrounding the deformation zone is used to generate empirical 'correction terms' in order to model the regional ionosphere. These corrections are then applied to the single-frequency data of the inner network to improve the accuracy of the results by modelling the residual atmospheric biases that would otherwise be neglected. This thesis reviews the characteristics of existing continuously operating GPS deformation monitoring networks. The UNSW-designed mixed-mode GPS-based volcano deformation monitoring system and the adopted data processing strategy are described, and details of the system's deployment in an inhospitable volcanic environment are given. A method to optimise the number of observations for deformation monitoring networks where the deforming body itself blocks out part of the sky, and thereby significantly reduces the number of GPS satellites being tracked, is presented. The ionosphere and its effects on GPS signals, with special consideration for the situation in equatorial regions, are characterised. The nature of the empirically-derived 'correction terms' is investigated by using several data sets collected over different baseline lengths, at various geographical locations, and under different ionospheric conditions. Data from a range of GPS networks of various sizes, located at different geomagnetic latitudes, including data collected on Gunung Papandayan, were processed to test the feasibility of the proposed mixed-mode deformation monitoring network approach. It was found that GPS baseline results can be improved by up to 50% in the midlatitude region when the 'correction terms' are applied, although the performance of the system degrades in close proximity to the geomagnetic equator during a solar maximum.