Infrasonic Observations of Earthquakes
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Infrasonic Observations of Earthquakes J. Paul Mutschlecner and R. W. Whitaker Los Alamos National Laboratory 2003 Infrasound Technology Workshop October 27-29, 2003 JaJolla, California. Opinions are those of the authors not of the US government. Overview.

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Infrasonic Observations of Earthquakes

J. Paul Mutschlecner and R. W. Whitaker

Los Alamos National Laboratory

2003 Infrasound Technology Workshop

October 27-29, 2003

JaJolla, California

Opinions are those of the authors not of the US government


Overview
Overview

  • Review infrasound signals from earthquakes

  • Understand infrasound signals with respect to earthquake characteristics

  • Provide estimate for earthquake infrasound signals

  • Discuss future directions - modeling and earthquake parameterization


Infrasound earthquake data set
Infrasound Earthquake Data Set

  • Number of earthquake events 30

  • Number of signals 47

  • Number of stations recording 4

  • 1983 - 2002

  • 13 multi-station detections

  • Analysis is ongoing



0.5-3.0 Hz data

2/22/02 M 5.7 32.38 N 115.35W

Channel data and Infra_Tool

Az Dev 1.7o



Data set characteristics1

< Dq > = 2.94 deg s = 2.33

< Dq> = 1.47 deg s =3.47

Data Set Characteristics


Data set characteristics2
Data Set Characteristics

<Dur> = 14.0 min s = 9.4

<f> = 0.84 Hz s = 0.49


Duration in min vs mb
Duration (in min) vs Mb

Examination of several other parameters

Shows no well defined trends

Possible indication of range dependence


Long signal duration for eq
Long Signal Duration for EQ

  • Source (EQ) duration

    • But most Earthquakes have motion over only a few seconds to a minute (aftershocks may contribute for larger Mb

  • Atmospheric propagation

    • Usual competition between pulse stretching and dissipation

    • HE signals of similar size have shorter durations

  • Source extension by seismic surface waves

    • Relation to magnitude supports this concept

    • Known cases of extended sources (eg Coalinga, 1983, and Northridge, 1994)

    • But for longest durations source must be ~100s km in diameter; and durations are not always symmetric about epicenter signal



Amplitude scaling for distance and stratospheric wind
Amplitude Scaling for Distance and Stratospheric Wind

Where

Vd - wind component directed, source to array

Vz - zonal component of stratospheric (50 km) wind

Vm - meridional component of stratospheric wind

q- azimuth to source

Distance and wind parameters are empirically derived

and b = 1.45 and k = 0.018

See: “An Empirical Study of Infrasound Propagation”, 1999, J. Paul Mutschlecner, Rodney W. Whitaker and Lawrence H. Auer, LA-13620-MS, Los Alamos National Lboratory


Scaled amplitude vs mb all events
Scaled Amplitude vs Mb(all events)

  • R2 = 0.591

  • = 0.419

    b = 0.454


Peak vertical velocity at 1 km and m l 40 events
Peak Vertical Velocity (at 1 km) and ML40 Events

  • R2 = 0.595

  • = 0.230

    b = 0.558

From: “Empirical Analysis of Near-Source Ground Motion,” 1980, A. F. Shakal and D. L. Bernreuter, NUREG/CR-2095 (UCRL-53028)



Statistical simulations
Statistical Simulations

{ } denote random variations


Results of statistical simulations
Results of Statistical Simulations

50 simulations

Monte Carlo approach


Summary
Summary

  • Relations determined

    • Log(Asc) vs Mb

    • Duration vs Mb

    • Frequency vs depth

  • Uncertainty sources identified and ~ match to observations

  • Better earthquake source parameterization needed

  • Source modeling being established





Close in ground motion velocities for 10 15 79 eq imperial valley 6 6
Close-in Ground Motion Velocities for 10/15/79 EQ, Imperial Valley (6.6)

From: “Empirical Analysis of Near-Source Ground Motion,” 1980, A. F. Shakal and D. L. Bernreuter, NUREG/CR-2095 (UCRL-53028)


Scaled amplitude for best wind data
Scaled Amplitude for Best Wind Data Valley (6.6)

  • R2 = 0.691

  • = 0.405

    b = 0.556


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