What’s the big fuss about Harmonic Tremor on Volcanoes? Jonathan M. Lees New Mexico Tech, 2009
Where is it observed? Karymsky, Kamchatka Arenal, Costa Rica Sangay, Ecuador Reventador, Ecuador Tungurahua, Ecuador *Santiaguito, Guatemala (Semeru, Merapi…others?)
http://www.seismo.com/msop/nmsop/13 volcano/volcano2/volcano2.html Typical VT event at Mt. Merapi, Indonesia a) typical example of a VT-B type event recorded during a high activity phase at Mt. Merapi. Note that the overall frequency content is mainly between 1 — 10 Hz with a dominant frequency at roughly 3 Hz. b) zoomed out version of the same event in its three components. Whereas the P-wave arrival is clearly visible, no clear S-wave arrival can be seen. The circle marks the wavelet that has the approximate S-wave travel time for the estimated source location
a) example of a LF-wave group recorded at Mt. Merapi. Clearly the dominant frequency is around 1 Hz. b) shows an example of a LF event recorded at two different sites located at Redoubt volcano, Alaska (courtesy of S. McNutt, Alaska Volcano Observatory; AVO). The spindle shaped signal is also known as Tornillo. Low Frequency Events
Harmonic tremor signal recorded at Mt. Semeru, Indonesia. Up to six overtones can be recognized starting with a fundamental mode located at roughly 0.8 Hz.
Typical Karymsky Chugging Event, 1997 Initial explosion Chugging Acoustic Vertical North-South East-West
Simple Harmonic Motion Sinusoid : 5 Hz (sample rate = 0.001)
Harmonic Tremor • Common on Volcanoes • Provides Constraints for Conduits: • Geometry • Composition • Density • Visco-elastic parameters
Many researchers have contributed to the study of Harmonic Tremor • K. Aki & M. Fehler • B. Crosson • B. Chouet • B. Julian • S. McNutt • M. Ripepe • V. Schlindwein • M. Hellweg • E. Gordeev • T. Ohminato • M. Garces • M. Yamamoto • H. Kumagai • T. Nishimura • R. Leet • K. Konstantinou (review) In this presentation we are concerned with tremor that is accompanied by infrasonic emission
Seismo-Acoustic Tremor:Chugging • Observed when seismic and acoustic waves are discerned and correlated • Examples: • Arenal(Benoit & McNutt, 1997; Garces, 1998; Hagerty et al. 2000) • Karmysky(Johnson & Lees, 1999; Lees et al. 2004) • Sangay (Johnson & Lees, 1999; Lees & Ruiz, 2008) • Reventador(Lees et al., 2008) • Tungurahua (Ruiz et al., 2005) • Fuego (Lyons et al.) • Santiaguito (Lees et al.)
Chugging Illustrated Slow Fast Video
Infrasound Chugging at Karymsky, 1997 While there are similarities between these chugging sequences, there is also considerable variability.
Chugging Spectrum Chugging Sound: Gliding
Karymsky Infrasound, 1997 Fundamental Mode….and Harmonics?
Numerous episodes of seismo-acoustic tremor exhibit fundamental frequencies ranging between 0.7 to 1.4 Hz. 21 chugging events at Karymsky
V = vertical I = Infrasound Santiaguito Explosion from 2009
V. Schlindwein M. Garces S. Mcnutt Others… J. Johnson J. Lees M. Hellweg M. Hellweg
Possible Physical Models • Harmonic Oscillations – Organ Pipe Modes? • Periodic Bubble/Slug Formation? • Flow Past Small Obstruction? • Cork/Viscous Plugging – Pressure Cooker Modes
Milton Garces’ Model: Organ Pipe Modes Arenal Volcano, Costa Rica
Organ Pipe Mode Explanation of Volcano Chugging Rijke Tube Excitation of fundamental modes And harmonics in a column of fluid
Resonating Cylindrical Conduits Integer Harmonics Odd Integer Harmonics Integer Harmonics Open-Open Open-Closed Closed-Closed
Correlation of interval time and amplitude: indication of non-linear, feed back mechanism Linear Trends Sangay Karymsky
Slope Analysis: Amplitude vs Time Delay Positive slopes Sangay, Ecuador Multiple Chugging Events
Chugging at Santiaguito: Linear amplitude-repose time until change in vent modifies relationship in time.
Pressure Cooker Model Steam Vent
Set of coupled, non-linear Differential Equations Lees and Bolton (1999) Damping Acceleration of plug Non-negative Ram effect Pressure in Pot Number of Molecules in Pot Pressure in Vent
Back of the envelope calculation plug Cone plug, radius R=20m, height h=20m Force = .2×109N Pressure = .1 MPa Pressure Cooker, Lees and Bolton, 1999