Introduction to Volcanic Seismology

Introduction to Volcanic Seismology Second edition Vyacheslav M. Zobin Observatorio Vulcanolo'gico, Universidad de Colima, Colima, Col., Mexico ELSEVIER AMSTERDAM BOSTON HEIDELBERG LONDON * NEW YORK OXFORD PARIS * SAN DIEGO SAN FRANCISCO SINGAPORE * SYDNEY TOKYO

Preface to the Second Edition Preface to the First Edition xiii xv 1 Introduction 1 1.1 Terms and Definitions 1 1.1.1 Volcanic Terms 1 1.1.2 Tectonic Terms 5 1.1.3 Seismological Terms 6 1.2 Subject of the Book 6 Acknowledgments 7 2 Seismicity at Volcanoes 9 2.1 History of Seismic Monitoring of Volcanic Activity 9 2.2 Classification of Volcanic Earthquakes 14 2.3 Sequences of Volcanic Earthquakes 20 2.3.1 Sequences of Volcano-Tectonic Earthquakes 20 2.3.2 Sequences of Eruption Earthquakes 27 3 Fundamentals of Volcanic Seismology 29 3.1 Magma Flow within the Volcanic Conduit 29 3.1.1 Magma Flow Regimes 30 3.1.2 Modeling of Magma Flow Regimes 31 3.2 Experimental Studies of the Volcanic Processes and Their Applications for the Seismic Sources 32 3.2.1 Experimental Grounds of the Brittle Fracturing in the Rocks at High Temperatures and High Pressure 32 3.2.2 Experimental Grounds of the Origin of Seismic Signals During the Magma Ascending Within the Volcanic Conduit 35 3.3 General Description of the Source of Seismic Signals at Volcanoes 41 3.3.1 Equivalent Force System Acting in the Earthquake Source 41 3.3.2 Green's Functions 41 3.3.3 Single Force 41 3.3.4 Seismic Moment Tensor 42 3.3.5 Waveform Inversion 43 4 Origin of Volcano-Tectonic Earthquakes 49 4.1 Migration of Magma and Its Seismic Potential 49 4.2 Volcanism and Tectonics 53 4.3 Source Nature of Volcano-Tectonic Earthquakes 59

4.3.1 Waveform and Spectra 59 4.3.2 Tensor Representation of the Source of Volcano-Tectonic Earthquake 61 4.4 Models of Volcano-Tectonic Earthquake Sequences 63 5 Volcano-Tectonic Earthquakes at Basaltic Volcanoes: Case Studies 67 5.1 Volcano-Tectonic Earthquakes Associated with Shield Volcanoes 67 5.1.1 Kilauea Volcano, Hawaii 67 5.2 Volcano-Tectonic Earthquakes Associated with Stratovolcanoes 71 5.2.1 Mount Etna, Sicily r 71 5.2.2 Oshima Volcano, Izu Islands 78 5.2.3 Klyuchevskoy Volcano, Kamchatka 79 5.3 Volcano-Tectonic Earthquakes Associated with Fissure Eruptions 82 5.3.1 New Tolbachik Volcanoes, Kamchatka 83 5.3.2 The 2005 2009 Ethiopia Rifting Episode 86 5.4 Volcano-Tectonic Earthquakes Associated with Caldera Collapse 90 5.4.1 Fernandina Volcano, Galapagos Islands 90 5.5 Volcano-Tectonic Earthquakes Associated with Submarine Eruptions 92 5.5.1 Teishi Knoll Volcano, Izu Islands 92 5.5.2 Miyakejima Volcano, Izu Islands 94 6 Volcano-Tectonic Earthquakes at Andesitic Volcanoes: Case Studies 99 6.1 Volcano-Tectonic Earthquakes Associated with Volcanic "Directed Blasts" 99 6.1.1 Bezymianny Volcano, Kamchatka 100 6.1.2 Sheveluch Volcano, Kamchatka 101 6.2 Volcano-Tectonic Earthquakes Associated with Phreatic and Phreato-Magmatic Explosions 105 6.2.1 El Chichon Volcano, Mexico 105 6.2.2 Volcan de Colima, Mexico 105 6.2.3 Popocatepetl Volcano, Mexico 107 6.2.4 Soufriere Hills Volcano, Montserrat 111 6.3 Volcano-Tectonic Earthquakes Associated with Lava Extrusions 115 6.3.1 Volcan de Colima, Mexico 115 6.4 Volcano-Tectonic Earthquakes Associated with Flank Eruptions 119 6.4.1 Sakurajima Volcano, Japan 119 7 Volcano-Tectonic Earthquakes at Dacitic Volcanoes: Case Studies 121 7.1 Volcano-Tectonic Earthquakes Associated with Summit Eruptions 121 7.1.1 Mount St. Helens, Cascades 121 7.1.2 Usu Volcano, Hokkaido 127 7.1.3 Unzen Volcano, Kyushu 129

vii 7.1.4 Pinatubo Volcano, Luzon 132 7.2 Volcano-Tectonic Earthquakes Associated with Flank Eruptions 136 7.2.1 Usu Volcano, Hokkaido 137 8 General Properties of Volcano-Tectonic Earthquake Swarms 145 8.1 Properties of Volcano-Tectonic Earthquake Swarms Inferred from the Data of Chapters 5 7 145 8.1.1 Temporal Variations 145 8.1.2 Spatial Distributions 148 8.1.3 Posteruption Seismic Activity 149 8.1.4 Duration of Seismic Swarms Prior to Eruption 150 8.1.5 Position of a Volcanic Event According to the Stage of Volcano-Tectonic Earthquake Swarm 150 8.2 Additional Data About Volcano-Tectonic Earthquake Swarm Properties 150 8.2.1 Size of Volcano-Tectonic Earthquake Swarm Area 150 8.2.2 Earthquake Swarm Duration 151 8.2.3 Magnitude Frequency Relations of Events in Volcano-Tectonic Earthquake Swarms 153 8.3 Some Regularities in the Volcano-Tectonic Earthquake Swarms Proclaiming Reawakening of Andesitic and Dacitic Volcanoes 156 8.3.1 Relationship Between the Duration of Stage 1 and the VEI of Forthcoming Explosion 158 8.3.2 Relationship Between the Duration of Stage 2 and Postexplosion Dome Building 159 8.3.3 The Conceptual Model of Reawakening Process 159 9 Source Properties of Volcano-Tectonic Earthquakes 161 9.1 Focal Mechanisms of Volcano-Tectonic Earthquakes: Double-Couple and Non-Double-Couple Models 161 9.1.1 Double-Couple Model 161 9.1.2 Non-Double-Couple Model 165 9.2 Source Spectral Characteristics of Volcano-Tectonic Earthquakes 168 9.2.1 Spectra of Total Records of Volcano-Tectonic Earthquakes 170 9.2.2 Spectral Source Characteristics of Volcano-Tectonic Earthquakes 171 9.3 Temporal Variations of the Source Spectral Characteristics and Focal Mechanisms of Volcano-Tectonic Earthquakes in the Course of Volcanic Activity 177 9.3.1 Corner Frequencies Variations 177 9.3.2 Stress-Drop Variations 180 9.3.3 Stress Field Rotations 182 9.4 Seismo-Tectonic Deformations in the Volcanic Region 182

10 Significant Volcano-Tectonic Earthquakes and Their Role in Volcanic Processes 189 10.1 Selection of Significant Volcano-Tectonic Earthquakes that Occurred in the Twentieth Century 191 10.2 Focal Rupturing of Significant Volcano-Tectonic Earthquakes and Its Role in Volcanic Processes 191 10.2.1 Rupturing of the Magnitude Mw 5.2 Earthquake Preceding the 1989 Teishi Knoll Submarine Eruption 193 10.2.2 Rupturing of the Magnitude Mw 7.1 Earthquake Preceding the 1996 Akademia Nauk Volcano Subaqual Eruption 195 10.2.3 Rupturing of the Magnitude Mw 5.6 Earthquake Preceding the 1996 Grimsv0tn Volcano Subglacial Eruption 196 10.3 The Magnitude 7 Volcano-Tectonic Earthquakes in Volcanic Processes 199 10.3.1 Event No. 2, Katmai, Alaska 200 10.3.2 Event No. 3, Sakurajima, Japan 201 10.4 Seismic Hazard of Significant Volcano-Tectonic Earthquakes 203 10.4.1 Maximum Magnitude M max 204 10.4.2 Attenuation of Earthquake Intensity with Distance for Volcanic Earthquakes 211 10.4.3 Recurrence Time 213 10.4.4 Estimation of the Seismic Hazard of Volcanic Activity of Volcan de Colima, Mexico 215 11 Origin of Eruption Earthquakes 217 11.1 Volcanic Processes Generating Seismic Signals of Eruption Earthquakes 217 11.1.1 Processes Within the Volcanic Conduit 217 11.1.2 Volcanic Flows 217 11.2 Source Mechanisms of Eruption Earthquakes 219 11.2.1 A Force System Equivalent to a Volcanic Eruption 219 11.2.2 Seismic Moment Tensors of Some Non-Double-Couple Sources of Eruption Earthquakes 222 11.3 Models of the Eruption Earthquake Sources 224 11.3.1 Models Based on the Vibration of Magma-Filled Structures 224 11.3.2 Models Based on Degassing Process of Magma 228 11.3.3 Modeling of Seismic Signals Generated by Pyroclastic Flows and Rockfalls 235 12 Volcanic Tremor 12.1 Seismograms and Spectra 12.2 Location of Volcanic Tremor 237 237 237

12.2.1 Oshima Volcano, Izu Islands 237 12.2.2 Etna Volcano, Sicily 238 12.3 Volcanic Tremors in Eruptive Process 238 12.3.1 Etna Volcano, Sicily 239 12.3.2 Pavlof Volcano, Alaska 240 12.3.3 Kilauea Volcano, Hawaii 241 12.3.4 Klyuchevskoy Volcano, Kamchatka 242 12.4 Relationship Between the Intensity of Volcanic Tremor and Volcanic Events 244 12.5 Special Cases of Volcanic Tremors 246 12.5.1 Isolated Tremors 246 12.5.2 Banded Tremor 252 12.5.3 Long-Period Tremor 256 12.5.4 Deep Tremor 258 13 Seismic Signals Associated with Pyroclastic Flows, Rockfalls, and Lahars 261 13.1 Occurrence of Pyroclastic Flows, Rockfalls, and Lahars During Volcanic Eruptions 261 13.2 Seismic Signals Associated with Pyroclastic Flows and Rockfalls: Waveforms and Spectra 261 13.2.1 Seismic Signals of Pyroclastic Flows Produced by the Partial Collapse of Lava Dome 263 13.2.2 Seismic Signals of Pyroclastic Flows Produced by the Collapse of Eruption Column 265 13.2.3 Seismic Signals of Pyroclastic Flows Produced by the Explosive Destruction of Growing Lava Dome 267 13.2.4 Seismic Signals Produced by Rockfall' 270 13.2.5 Spectral Characteristics 272 13.3 Occurrences of Earthquakes Associated with Pyroclastic Flows and Rockfalls 273 13.4 Relationship Between the Pyroclastic Flow and Rockfall Earthquakes and Seismo-Volcanic Activity During Lava Emission 273 13.5 Quantification of Pyroclastic Flow and Rockfall Earthquakes 276 13.5.1 Quantification of Pyroclastic Flow and Rockfall Earthquakes Occurring Due to Partial Collapse of the Lava Dome and Recorded by Short-Period Instruments at Volcan de Colima, Mexico 278 13.5.2 Relationship Between the Magnitude of Pyroclastic Flow and Rockfall Earthquakes and the Volume of Pyroclastic Flows 280 13.5.3 Relationship Between the Amplitude of Long-Period Records of Pyroclastic Flow and Rockfall Earthquakes and the Volume of Pyroclastic Flows 281

13.6 Location Pyroclastic Flows Using the Amplitude Signals of Earthquakes 282 13.7 Seismic Signals Associated with Lahars: Waveforms and Spectra 282 13.8 Seismic Signals as a Source of Information About the Lahar Structure 287 13.9 Seismic Tracking of Lahars 290 13.10 Comparison of the Seismic Characteristics of Pyroclastic Flows and Lahars 292 14 Seismic Signals Associated with Volcanic Explosions 295 14.1 Waveforms and Spectra 296 14.1.1 Strombolian Explosions 296 14.1.2 Vulcanian Explosions 297 14.1.3 Phreato-Magmatic Explosions 297 14.2 Nature of the Seismic Signals of Explosive Earthquakes 299 14.2.1 Comparison of the Contemporary Video and Seismic Records During an Explosion 299 14.2.2 Type of Waves Composing the Seismic Signal of an Explosion 302 14.3 Sources of Explosion Earthquakes and Their Quantification 305 14.3.1 Multiple Source of Explosions 307 14.3.2 Two-Stage Model of Explosive Process 311 14.3.3 Relationship Between the Seismic Moment of Preliminary LP Phase and the Energy of Explosions for Sakurajima Volcano 314 14.3.4 Volcanic Explosive Process as a Source of Hybrid Earthquakes 318 14.4 Location of Explosion Earthquakes 318 14.4.1 Location of the Initial Sub-Events from Waveform Inversion 318 14.5 Explosion Sequences 319 14.6 Explosion Earthquakes in Eruptive Process 322 15 Long-Period and Very Long-Period Seismic Signals at Volcanoes 327 15.1 Waveforms and Spectra 327 15.1.1 Long-Period Seismic Signals 327 15.1.2 Very Long-Period Seismic Signals 328 15.1.3 Occurrences of LP and VLP Events 331 15.1.4 Nature of LP and VLP Seismic Signals 334 15.2 Geometry of the Sources of LP and VLP Seismic Signals 337 15.3 Type of Fluid Within the Fluid-Filled Cracks 339 15.3.1 Crack Model 340 15.3.2 Complex Frequencies of the LP Seismic Signal for Different Fluids 341

xi 15.3.3 Identification of the Type of Fluid from LP Seismic Signals 341 15.4 Location of the Sources of LP and VLP Events 347 15.5 Conceptual Models of the Relationship Between the Sources of the LP and VLP Seismic Signals and Their Role in Eruptive Process 351 16 Swarms of Microearthquakes Associated with Effusive and Explosive Activity at Volcanoes 355 16.1 Waveforms and Spectra 355 16.2 Structure of Microearthquake Swarms 357 16.3 Microearthquake Swarms in Eruption Process 362 16.3.1 Kizimen volcano, Kamchatka 362 16.3.2 Stromboli volcano, Aeolean Islands 364 16.3.3 Mount St. Helens, Cascades 366 16.3.4 Ubinas volcano, Peru 367 16.3.5 Volcan de Colima, Mexico 368 16.4 Nature of Microearthquakes 371 16.4.1 Similarity Between the Microearthquake Waveforms and the Seismic Signals Well-Associated with the Volcanic Events 371 16.4.2 Quantification of Microearthquakes 375 16.4.3 Nature of Microearthquakes Resolved from Waveform Inversion 380 17 Acoustic Waves Generated by Volcanic Eruptions 381 17.1 Infrasonic Acoustic Waves from Small Volcanic Explosions (VEI 1 and 2) 381 17.1.1 Waveforms and Spectra 382 17.1.2 Families of Infrasonic Signals 383 17.1.3 Source Location of the Infrasonic Events 383 17.1.4 Relationship Between the Amplitudes of the Seismic and Infrasonic Signals 386 17.2 Long-Period Acoustic and Acoustic-Gravity Waves from Large Volcanic Explosions (VEI 4 6) 390 17.2.1 Near-Field Waveforms of the Long-Period Acoustic Waves 390 17.2.2 Far-Field Registrations of the Long-Period Acoustic Waves 391 17.3 Acoustic Waves Produced by the Lava Dome Collapse and the Propagation of Pyroclastic Flow and Rockfalls 393 17.3.1 Dome Collapse 393 17.3.2 Pyroclastic Flow Propagation 395 17.3.3 Large Rockfall Propagation 398

17.4 Acoustic Waves Produced During Volcanic Microearthquake Swarms ("Drumbeats") 399 17.5 Utility of the Acoustic Signals for Volcano Activity Monitoring 401 17.5.1 Estimation of the Energy of Eruptive Events 401 17.5.2 Reconstruction of the Process of Dome Collapses and Pyroclastic Flow Movement 403 17.5.3 Monitoring of Phreatic and Strombolian Explosions 405 18 Seismic Monitoring of Volcanic Activity and Forecasting of Volcanic Eruptions 407 18.1 Methodology of Seismic Monitoring of Volcanic Activity 407 18.1.1 Seismic Networks Around Volcanoes 407 18.1.2 Initial Processing of Seismic Data 410 18.1.3 Automatic Classification of the Seismic Signals 412 18.1.4 Location of Seismic Events 416 18.2 Applications of Volcanic Seismicity to the Forecasting of Volcanic Eruptions and Predicting of Volcanic Hazards 416 18.2.1 Methods Based on the Statistical Variations in the Parameters of Volcano-Tectonic Earthquakes 417 18.2.2 Chronicle of Some Forecasting of Volcanic Eruptions Based on Seismic Monitoring 424 19 Seismic Activity at Dormant Volcanic Structures: A Problem of Failed Eruption 433 19.1 Failed Eruptions: Case Studies 433 19.1.1 Failed Eruptions at Large Calderas 433 19.1.2 Failed Eruptions at Strato-Volcanoes 437 19.1.3 Failed Eruptions in Rift Settings 440 19.2 Modeling of Magma Ascent Resisting 445 19.2.1 Experimental Study of the Ascent of a Fixed Magma Volume 446 19.2.2 Arrest of Propagating Dyke Due to Mechanical Barriers and Density Stratification in an Upper Crustal Horizon 447 19.3 Monitoring of the Seismic Activity at Dormant Volcanoes 451 19.3.1 Monitoring of Andesitic and Dacitic Dormant Volcanoes 452 19.3.2 Monitoring of Basaltic Dormant Volcanoes 453 References 457