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Pattern and process in volcano seismology Item Type Thesis Authors Benoit, John Paul Download date 04/10/2021 14:14:58 Link to Item http://hdl.handle.net/11122/9464 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type o f computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. 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PATTERN AND PROCESS IN VOLCANO SEISMOLOGY A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By John Paul Benoit, B.S. Fairbanks, Alaska May 1998 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 9838831 Copyright 1998 by Benoit, John Paul All rights reserved. UMI Microform 9838831 Copyright 1998, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PATTERN AND PROCESS IN VOLCANO SEISMOLOGY By John Paul Benoit RECOMMENDED: . _ s L " 's' Prcif. Max Wyss. - ProLJohn Eicfaelbereer / jc I- /4 c? > ^ ^ - l5r. Roger Hansen, State Seismologist Research Prof. Stephen McNutt. Advisory Comfnltfee Chair Associate Prof. Paul Layer. \i Department Head /i / APPROVED: Prof. Paul Reichardt, Dean, College of Natural Science. Engineering, and Mathematics Prof. Joseph Kan. Dean of the Graduate School Date Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT The patterns of occurrence and the underlying processes of two important seismological phenomena at volcanoes, earthquake swarms and volcanic tremor, were investigated. A global database of volcanic earthquake swann parameters was compiled and was used to evaluate the March 10-14,19% seismo-volcanic crisis at Akutan Volcano, Alaska. Earthquake swarm durations and magnitudes were compared with eruptive activity using this database. Trends identified using the database suggest that the Akutan swarm was not precursory and, no eruption occurred. We postulate that a deep intrusion with a large opening component occurred under the flanks of Akutan. The global swarm database has provided an important baseline and has proved to be useful in preparing eruption scenarios for public information releases. The duraiion-amplitude distribution or ffequency-size scaling of volcanic tremor was also examined. The hypothesis tested was that the duraiion-amplitude distribution may be approximated by an exponential function. The exponential model, implying a scale-bound source process, is found to be a better fit to data then a power-law (scale invariant) model. The exponential model gives a satisfactory description of tremor associated with a wide range of volcanic activity. We propose that exponential scaling of tremor amplitude is due to fixed source geometry driven by a variable excess pressures. This implies that the characteristic amplitude of the duration-amplitude distribution is proportional to a geometric dimension of the source. Broadband seismic data recorded at Arenal volcano, Costa Rica, provide new constraints on tremor source processes. Arenal's tremor contains as many as seven harmonics, whose frequencies vary temporally. This source is inferred to be a shallow, 200-660 m-long resonator, radiating seismic energy from displacement antinodes. We infer that the resonator is gas- charged magma with variable bubble concentration within the conduit and also changes as a function of time, thereby changing the acoustic velocity and the boundary conditions. Polarization analyses for the fundamental mode show particle motion azimuths abruptly rotating, which may be explained by a decrease in incidence angle near the recording site. We suggest that energy for this mode is radiated predominantly from a displacement antinode that is changing position with time. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iv Table of Contents Abstract “* Table of Contents *v List of Figures “ List of Tables » i Acknowledgements Chapter 1 Thesis Introduction 1.0 General Introduction I 1.1 An overview of the chapters 3 1.2 References 6 Chapter 2 Use of a global database of volcanic earthquake swarms during the 1996 seismo-volcanic crisis at Akutan volcano, Alaska 2.0 Abstract 7 2.1 Introduction . 8 23 Global Volcanic Earthquake Swarm Database (GVESD) 10 2_3 Results from the GVESD 11 2.3.1 Swann duration 12 2.3.2 Swann duration and eruption explosivity 15 2.3.3 Event type and swarm duration 17 2.3.4 The largest shock within a volcanic earthquake swarm (Mmax) 18 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V 2.3.5 Mmax and the explosivity of the following eruption 21 2.4 A case study: Using the GVESD during the 1996 Akutan crisis 23 2.4.1 Description of the Akutan swarms 23 2.5 Discussion 28 2.6 Conclusions 39 2.7 Acknowledgements 42 2.8 References 42 Appendix 2A Development and Description of the Global Volcanic Earthquake Swarm Database 2A.1 Introduction 47 2A.2 Database Structure and Description 49 2AJ2.1 Volcano Table 50 2A.22 Earthquake Swarm Table 50 2A.23 Eruption Table 50 2A3 VOLCAT Organization and Parameter Description 51 2A.3.1 Morphology. Tectonic Framework. Elevation, and Edifice Relief 53 2A.32 Range of Erupted Products 55 2A.4 SWARMCAT Organization and Parameter Description 56 2A.4.1 Swarm Dates. Durations and Uncertainties 57 2A.4.2 Definition of a Swarm and Swarm Duration 57 2A.43 Swarm Type 58 2A.4.4 Event Types 60 2A.43 Quality Grades 61 2A.4.6 Maximum Magnitude. Intensity, and Depth 62 2A.4.7 Cumulative Energy. Energy Release Rate, and Repose 63 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vi 2A.4.8 Earthquake Counts and Magnitude Detection Threshold 63 2A.4.9 Seismograph Information 63 2A.4.10 Previous Swarms and Other Reported Information 64 2A.4.11 References, Comment and Key Phrase fields 65 2A3 ERUPTCAT Organization and Parameter Description 65 2A.5.1 Data Sources 69 2A.5 2 Erupted Volume. Plume Height. Silica Content, and the VE2 70 2A.6 Improvements and Future Work 71 2A.7 Acknowledgements 71 2A.8 References 72 Chapter 3 The Duration-Amplitude Distribution of Volcanic Tremor 3.0 Abstract 74 3.1 Introduction 75 32 Frequency-size distributions 77 33 Methodology 78 3.4 Case studies 86 3.4.1 Crater Peak. Mt. Spurr. Alaska 86 3.4.2 Kilauea. Hawaii 90 3.4.3 Karkar and Ulawun, Papua New Guinea 93 3.4.4 Pavlof. Alaska 96 3.43 Fuego. Guatemala and Arenal. Costa Rica 97 3.4.6 Old Faithful Geyser. Yellowstone National Park. Wyoming 99 3.4.7 Redoubt. Alaska 101 33 Is volcanic tremor a series of law-fireqnency events closely spaced in time? 102 3.6 Discussion 106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.7 Conclusions 112 33 Acknowledgements 112 3.9 References 113 Appendix 3A 3A.1 Definition of reduced displacement 119 3AJ2 Calculation of reduced displacement from RSAM data 119 Appendix 3B 3B.1 Overestimation of RMS ground displacement using helicorders or RSAM data 122 Appendix 3C 3C.1 The duration-amplitndewaling of acoustic signals at Arenal volcano 125 3G2 Data 125 3C_3 Duration-amplitude measurements 125 Chapter 4 New Constraints on Source Processes of Volcanic Tremor at Arena! Volcano. Costa Rica, Using Broadband Seismic Data 4.0 Abstract 128 4.1 Introduction 129 42 Analyses and Results 133 43 Discussion and Conclusions 142 4.4 Other Observations and Future Work 149 45 Acknowledgements 150 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. viii 4.6 References 150 Appendix 4A 4A.1 Calculation of theoretical dispersion curves of Love waves 154 4A3 Source code 155 Chapter 5 Thesis Condusion 5.0 General Conclusions 159 5.1 Volcanic Earthquake Swarms 159 52 Volcanic

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