INTRODUCTION TO VOLCANIC SEISMOLOGY V.M. Zobin Observatorio Vulcanologico, Colima, Mexico ELSEVIER Amsterdam - Boston - Heidelberg - London - New York - Oxford Paris - San Diego - San Francisco - Singapore - Sydney - Tokyo
vii Contents Chapter 1 1 Introduction 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 7 1.3. Acknowledgements 7 Chapter 2 9 Seismicity at Volcanoes 2.1. History of seismic monitoring of volcanic activity 9 2.2. Classification of volcanic earthquakes 16 2.3. Sequences of volcanic earthquakes 19 2.3.1. Sequences of volcano-tectonic earthquakes 21 2.3.2. Sequences of eruption earthquakes 28 Chapter 3 31 Origin of Volcano-tectonic Earthquakes 3.1. Magma and its physical and chemical properties 32 3.2. Volcanism and tectonics 35 3.3. Models of volcano-tectonic earthquake sequences 42 Chapter 4 47 Origin of Eruption Earthquakes 4.1. Processes of the outlet of eruption products from volcanic 47 crater 4.1.1. Fragmentation of magma 47 4.1.2.-Volcanic "fall-and-flow" processes 48 4.2. Seismic modeling of eruption earthquakes 50 4.2.1. Model of seismic signals produced by an eruption 51 4.2.2. Models based on the vibration of magma body 54 4.2.3. Models based on degassing process of magma 59 4.2.4. Modeling of seismic signals generated by pyroclastic 64 flows and rockfalls
viii Contents Chapter 5 67 Volcano-tectonic Earthquakes at Basaltic Volcanoes 5.1. Volcano-tectonic earthquakes associated with shield 67 volcanoes 5.1.1. Kilauea volcano, Hawaii 67 5.1.2. Mt. Etna, Sicily 73 5.2. Volcano-tectonic earthquakes associated with 77 stratovolcanoes 5.2.1. Oshima volcano, Izu islands, Japan 77 5.2.2. Klyuchevskoy volcano, Kamchatka, Russia 79 5.3. Volcano-tectonic earthquakes associated with fissure 81 5.3.1. New Tolbachik Volcanoes, Kamchatka, Russia 81 5.4. Volcano-tectonic earthquakes associated with caldera 86 collapse 5.4.1. Fernandina volcano, Galapagos Isl. 87 5.5. Volcano-tectonic earthquakes associated with submarine 89 5.5.1. Teishi-Knoll volcano, 1989. Izu Islands, Japan 89 Chapter 6 93 Volcano-tectonic Earthquakes at Andesitic Volcanoes 6.1. Volcano-tectonic earthquakes associated with volcanic 93 "directed blasts" 6.1.1. Bezymianny volcano, Kamchatka, Russia 94 6.1.2. Sheveluch volcano, Kamchatka, Russia 97 6.2. Volcano-tectonic earthquakes associated with phreatic and 100 phreato-magmatic explosions 6.2.1. El Chichon volcano, Mexico 100 6.2.2. Volcan de Colima, Mexico 102 6.2.3. Soufriere Hills volcano, Montserrat 104 6.3. Volcano-tectonic earthquakes associated with lava 110 extrusions 6.3.1. Volcan de Colima, Mexico 110 6.4. Volcano-tectonic earthquakes associated with flank 113 eruption 6.4.1. Sakurajima volcano, Japan 113 Chapter 7 115 Volcano-tectonic Earthquakes at Dacitic Volcanoes 7.1. Volcano-tectonic earthquakes associated with central 115 7.1.1. Mt. St. Helens, Cascades, U.S.A 115 7.1.2. Usu volcano, Hokkaido, Japan 119
ix 7.1.3. Unzen volcano, Kyushu, Japan - 121 7.1 A. Pinatubo volcano, Philippines 125 7.2. Volcano-tectonic earthquakes associated with flank 129 Chapter 8 133 General Properties of Volcano-tectonic Earthquake Swarms 8.1. Properties of volcano-tectonic earthquake swarms inferred 133 from the data of Chapters 5 to 7 8.1.1. Temporal variations 133 8.1.2. Spatial distributions 136 8.1.3. Post-eruption seismic activity 137 8.1.4. Duration of seismic activity before volcanic event 138 8.1.5. Position of a volcanic event according to the stage of 138 volcano-tectonic earthquake swarm 8.2. Additional data about volcano-tectonic earthquake swarm 139 properties 8.2.1. Size of volcano-tectonic earthquake swarm area 139 8.2.2. Earthquake swarm duration 140 8.2.3. Magnitude-frequency relations of events in volcano- 141 tectonic earthquake swarms Chapter 9 145 Source Properties of Volcano-tectonic Earthquakes 9.1. Focal mechanisms of volcano-tectonic earthquakes: double 145 couple and non-double couple models 9.1.1. Double couple model 146 9.1.2. Non-double couple model 152 9.2. Spectral characteristics of volcano-tectonic earthquakes 156 9.2.1. Spectra of total records of volcano-tectonic 157 earthquakes 9.2.2. Spectral source characteristics of volcano-tectonic 158 earthquakes and their relationship with the type of volcanic activity 9.2.3. Temporal variations of spectral source characteristics 161 of volcano-tectonic earthquakes in the course of volcanic activity 9.3. Seismo-tectonic deformations in volcanic region 165 Chapter 10 171 Significant Volcano-tectonic Earthquakes and their Role in Volcanic Processes 10.1. Selection of significant volcano-tectonic earthquakes that 172
occurred in the XXth century 10.2. Focal rupturing of significant volcano-tectonic 175 earthquakes and its role in volcanic processes - 10.2.1. Rupturing of the magnitude Mw 5.2 earthquake 176 preceding the 1989 Teishi Knoll submarine eruption 10.2.2. Rupturing of the magnitude Mw 7.1 earthquake 178 preceding the 1996 Akademia Nauk volcano subaqual eruption 10.2.3. Rupturing of the magnitude Mw 5.6 earthquake 181 preceding the 1996 Grimsvotn volcano subglacial eruption 10.3. The magnitude 7 volcano-tectonic earthquakes in volcanic 183 processes 10.3.1. Event No 2, Katmai, Alaska 183 10.3.2. Event No 3, Sakurajima, Japan 186 10.4. Seismic hazard of significant volcano-tectonic earthquakes 186 10.4.1. Maximum magnitude Mmax 188 10.4.2. Attenuation of intensity with distance for volcanic 192 earthquakes 10.4.3. Recurrence time 194 10.4.4. Estimation of seismic hazard of volcanic activity of 196 Colima volcano, Mexico Chapter 11 197 Volcanic Tremor 11.1. Seismograms and spectra 197 11.2. Location of volcanic tremor 197 11.2.1. Oshima volcano, Izu islands 197 11.2.2. Kilauea volcano, Hawai 198 11.3. Volcanic tremors in eruptive process 200 11.3.1. Etna volcano, Italy 200 11.3.2. Pavlof volcano, Alaska 201 11.3.3. Kilauea volcano, Hawai 201 11.4. Relationships between the intensity of seismic signals and 202 volcanic events 11.5. Special cases of volcanic tremors 205 11.5.1. Isolated tremors 205 11.5.2. Deep tremor 208 11.5.3. Long-period tremor 210 Chapter'12 213 Earthquakes Related to Pyroclastic Flows and Rockfalls 12.1. Occurrences of "fall-and-flow" earthquakes 213 12.2. Relationship between the "fall-and-flow'' earthquakes and 215 seismo-volcanic activity during lava emission 12.3. Quantification of "fall-and-flow" earthquakes 217
xi 12.3.1. Quantification of "fall-and-flow" earthquakes 217 recorded by short-period instruments at Volcan de Colima, Mexico 12.3.2. Relationship between the amplitude of the long- 222 period records of "fall-and-flow" earthquakes and the volume of pyroclastic flows 12.4. Location pyroclastic flows using amplitude signals of "fall- 224 and-flow" earthquakes Chapter 13 227 Explosion Earthquakes 13.1. Waveforms of explosion earthquakes 227 13.2. Occurrences of explosion earthquakes and their location 229 13.3. Explosion earthquakes in the eruptive process 232 13.4. Size of explosion earthquakes 233 Chapter 14 235 Seismic Monitoring of Volcanic Activity and Prediction of Volcanic Eruptions 14.1. Methodology of seismic monitoring of volcanic activity 225 14.2. Applications of volcanic seismicity in the prediction of 241 volcanic 14.2.1. Methods based on the statistical variations in the 243 parameters of volcano-tectonic earthquakes 14.2.2. Methods based on a study of the variations in 249 complex behavior of different types of volcanic earthquakes 14.2.3. Seismic precursors to small explosions 250 Chapter 15 253 Some Remarks About Unresolved Problems 15.1. Variety of low-frequency volcanic earthquakes 253 15.1.1. Low-frequency volcano-tectonic earthquakes 253 15.1.2. Low-frequency eruption earthquake s 257 15.2. Seismic activity at dormant volcanic structures: 258 A problem of possible eruption 15.2.1. Matsushiro swarms 258 15.2.2. Long Valley swarms 260 15.2.3. Campi Flegrei swarms 261 References 265 Index of Volcanic Events 285