Anthony Lomax - Science

Recent papers and meeting presentations

Earthquake Location

Non-linear, Global Search Earthquake Location in 3D structures - NonLinLoc

I work on non-linear, global-search algorithms for probablilistic earthquake location in 3D structures. Location in 3D is important both for the development and study of 3D earth models and can lead to more accurate earthquake locations. Non-linear, global-search location gives a relatively complete picture of the location uncertainties; this is particularly important for depth determinations and for event locations outside of a station network. You can see a poster comparing linear and non-linear locations, and we have a book chapter on the global search methods. You may try the Seismicity Viewer applet to examine global-search locations for Vesuvius volcalno and for the 1995 Vintimiglia, Italy earthquake sequence. You can download a software package called NonLinLoc for Non-linear, Global Search Earthquake Location in 3D structures.

I am additionally working on

an Equal Differential Time location likelihood function that is much more robust in the presence of outliers than the usual, root-mean-square, L2 norm (algorithm description).
a new oct-tree importance sampling method for fast and accurate determination of probablilistic earthquake locations (algorithm description).
experimental design applet for a seismic network - a Java applet tool for determining which of a set of potential new receivers are likely to most improve the capability of a local or regional seismic network to monitor given seismic source regions.
extending NonLinLoc to spherical coordinates to allow regional and teleseismic locations and to support re-locaton of early-instrumental earthquakes.

The global-search location algorithms and supporting programs are available in the software package NonLinLoc

Path-summation Waveforms

Fast calcualtion of approximate waveforms in 3D

I have been continuing work on a path-summation method for very-fast modeling of acoustic waves in realistic, 3-D earth-structures using an analogue of Feynman path-integrals. The path-summation approach is approximate, but reproduces finite-frequency wave phenomena such as diffractions. It requires insignificant computer memory and, depending on the number of waveforms required, up to one to two orders of magnitude less computing time than finite differences. The speed and accuracy of the path-summation method may be sufficient to allow 3D, waveform inversion using stochastic, non-linear, global search methods.

Other research work

Waveform systhesis, surface wave inversion, global-search optimization, ...

I have completed work on something called the Wavelength-Averaging method for rapid simulation of wave propagation in complicated media. I also have extended my work on genetic algorithm inversion of surface waves to give a better search of the model space and to produce probabilistic results. This has lead to work investigating how to find acceptable solutions for complicated misfit functions and the development of Monte-Carlo importance sampling methods to estimate likelihood functions in the model space. You can see more details in the abstracts for Recent papers and meeting presentations with which I have been invlolved.

Internet based Java software

Powerful, interactive visualisation and analysis tools for the Internet. (see my Software home page)

A Java program (applet) for viewing earthquake locations and other data in 3D. Try this Seismicity Viewer applet to examine grid-search locations for the 1995 Vintimiglia earthquake sequence.

An applet for viewing 3-component seismograms. You can use this Seismogram Viewer applet to examine a 3-component, broadband recording of an earthquake in Southern Italy.

An experimental design applet for a seismic network - a Java applet tool for determining which of a set of potential new receivers are likely to most improve the capability of a local or regional seismic network to monitor given seismic source regions.

I am involved in a project "Sismo des Ecoles" which places seismometers in schools and allows the students to manage and analyze the seismic data using PC's and the web.

	Special Topics
	2020 Puerto Rico seismicity Calibrated, absolute location of 2020 Puerto Rico seismicity
	July 2019 M7.1 Ridgecrest (California) earthquake sequence Absolute location of 2019 Ridgecrest seismicity reveals duplex Mw6.4 ruptures, migrating and pulsing Mw7.1 foreshocks, and unusually shallow Mw7.1 nucleation
	April 25, 2015 M7.8 Nepal (Gorkha) earthquake Daily seismograms since 25 April 2015 M7.8 Nepal earthquake mainshock at station EVN-Everest Mainshock ground motion at station KATNP in Kathmandu (video animations of particle motions) Aftershocks, back-projections, InSAR, etc in Google Earth (kml) Disaster Response: Information within first hour suggests rupture zone and shaking intensity
	Rapid Earthquake Analysis Early-est, tsunami early warning, and rapid magnitudes for large earthquakes Mw9 Tohoku, Japan Earthquake and Tsunami, 11 March 2011, 05:46 UTC (Early-est) Tsunami early warning using earthquake rupture duration and P-wave dominant-period (Early-est) Tsunami early warning using earthquake rupture duration Mwpd: A Duration-Amplitude Procedure for Rapid Determination of Earthquake Magnitude and Tsunamigenic Potential from P Waveforms An energy-duration procedure for rapid and accurate determination of earthquake magnitude and tsunamigenic potential
	California Earthquake of 18 April, 1906 Definition of Hypocenter: Location of the Focal Region and Hypocenter of the California Earthquake of April 18, 1906 Papers: Location and Tectonics of the Focal Region of the California Earthquake of 18 April 1906, Bull. Seism. Soc. Am., 2008. (abstract; local copy of Electronic Supplement) A Reanalysis of the Hypocentral Location and Related Observations for the Great 1906 California Earthquake, Bull. Seism. Soc. Am., 2005. (abstract; local copy of Electronic Supplement) Lomax and Bolt, Broadband waveform modeling of anomalous strong ground motion in the 1989 Loma Prieta earthquake using three-dimensional geologic structures, Geophys. Res. Lett., 1992. (view PDF)
	2004 Sumatra-Andaman Islands Earthquake Rapid estimation of faulting extent for large earthquakes by locating the end of rupture: application to the 2004, Mw=9.0 South Asia mega-thrust, European Geosciences Union, April 2005, Vienna. Rupture during 8 minutes propagating to the NNW for the 2004 Sumatra-Andaman Islands Earthquake - is this earthquake larger than the 1960 Chile earthquake?