Masteropgave. / Format: PDF. Bibl.

Master's thesis. / Format: PDF. Bibl.

Hovedopgave. / Format: PDF. Bibl.

Masteropgave. / Format: PDF. Bibl.

Master's thesis. / Format: PDF. Bibl.

Thesis (D. Min.)--Logos Evangelical Seminary, 2002. / Vita. Includes bibliographical references (leaves 256-286).

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 206-217).

Telica Volcano, Nicaragua, is a persistently restless volcano with high rates of seismicity that can vary from less than ten events to over a thousand events per day. Low-frequency (LF) events dominate the seismic catalogue and seismicity rates at Telica show little clear correlation with periods of eruption. As such, traditional methods of forecasting of volcanic activity based on increases in seismicity and recognition of LF activity are not applicable. A single seismic station has been operating at Telica since 1993, and in 2010 we installed a broadband seismic and continuous GPS network (TESAND network) at Telica. In this study we investigate the seismic characteristics surrounding a nine-month period of phreatic to phreatomagmatic explosions in 1999, and also from the initial three-and-a-half year deployment of the TESAND network, including a three-month phreatic vulcanian eruptive period in 2011. We demonstrate that pertinent information can be obtained from analysis of single-station data, and while large seismic networks are preferable when possible, we note that for many volcanoes this is not possible. We find unusual patterns of seismicity before both eruptive periods; rather than a precursory increase in seismicity as is observed prior to many volcanic eruptions, we observe a decrease in seismicity many months prior to eruption. We developed a new program for cross-correlation of large seismic data catalogues and analysed multiplet activity surrounding both eruptive periods. We observed that the formation of new multiplets corresponds to periods of high event rates (during inter-eruptive periods) and high percentages of daily events that belong to a multiplet. We propose a model for the seismicity patterns observed at Telica, where changes in seismicity are related to a cyclic transition between open-system degassing and closed-system degassing. Periods of open-system degassing occur during non-eruptive episodes and are characterised by high event rates, a broad range of frequency content of events and high degrees of waveform correlation. A transition to closed-system degassing could be due to sealing of fluid pathways in the magmatic and/or hydrothermal system, or due to magma withdrawal. Periods of closed-system degassing are characterised by low event rates, higher frequency contents and low degrees of waveform correlation. Eruptive periods may then represent a transition from closed-system degassing to open-system degassing, however the system must also be capable of transitioning to open-system degassing without eruption. These observations have important implications for volcano monitoring and eruption forecasting at persistently restless volcanoes. Rather than a precursory increase in seismicity as is often observed prior to eruption at other volcanoes, our observations indicate that phreatic eruptions at Telica occur after a decrease in seismicity, a corresponding change in the frequency content of events, and a decrease in waveform correlation. These changes may represent a period of closed-system degassing that could culminate in phreatic eruptions. The inclusion of real-time analysis of variations in frequency content and multiplet activity provides critical information for volcano monitoring institutions.

Existing and novel laboratory techniques and equipment are used to produce comprehensive information on the liquefaction mitigation provided by granular drainage columnar inclusions in loose sand. Extensive use is made of bender-element testing techniques and the frequency dependence of such measurements is examined. Phase-sensitive detection is proposed as a new method to obtain the frequency response of the element data. The applicability of this technique is extended to provide a convenient and accurate method for determination of the time-of-flight of a shear-wave in sand. This technique is employed to measure the load share between sand and columnar components during triaxial testing. A novel low cost, high loading frequency, triaxial testing system is developed and preliminary testing is carried out on both pure sand samples and composite columnar samples. The testing programme examines aspects of liquefaction mitigation due to the rigidity of the columnar inclusions and due to the increased permeability of the columns. The laboratory results are verified by the application of existing analytical models. The equipment and techniques are used to investigate the feasibility of using recycled aggregates in place of stone backfill.

The purpose of this study is to explore, compare, and analyze the process of learning and the importance of adaptation and resilience in a continuously evolving environment amidst natural disasters as seen in two earthquake-prone communities located in southern Peru. The framework of complex adaptive systems offers insight into understanding human limitations to control an environment that is constantly far from equilibrium. Complexity science theory supports the study and the self-organization of communities in the process of coping with a disaster. Reports generated from informal interviews and participatory techniques further support all evidential findings. The co-evolution process given by the participation of diverse agents may include the collaboration and involvement of victims as well as local, state, and national organizations. Results from the co-evolution process may derive from previous experiences, preparedness, education, the development of previous relationships, and the capacity of improvisation. Furthermore, solidarity, self-organization and adaptation of agents in a community may further influence the ability to deal effectively with unexpected adversity. / text