Charles A. Langston

Research

I have been interested in what information seismic wave forms can give for both Earth's velocity structure and the nature of artificial and natural seismic sources. My early work centered around modeling of teleseismic body waves for determining source depth and orientation through dislocation source, then moment tensor source formulations. Teleseismic receiver function research grew out of the observation that teleseismic P wave forms carried hints of crustal velocity structure through Ps reverberations and conversions at the receiver. This research expanded through the work of many students to include teleseismic shear-coupled PL waves, regional PnL waves, Pn, Pg, and Lg regional waves, multimodal Rayleigh and Love waves, high frequency local waves, strong ground motions, and broadband regional wave forms as a whole. The search for meaning in the "wiggle" of a seismogram led to investigating signal processing methods that can extract important wave attributes directly from the seismogram so this information could be used to constrain source and structure models. These techniques include testing of novel phased array geometries, wave gradiometry, and continuous wavelet transform methods. Perhaps most importantly, these excursions into new signal processing directions were driven by the data collected in really interesting and fun seismic deployments, not all my own, in Africa, the Central United States, and southern California. Estimation of wave gradients through wave gradiometry naturally led to examining new strain and rotation seismic data. In addition, exposure to data from the New Madrid Cooperative Seismic Network extended my interest from sources within the Earth to those within the atmosphere and the associated problems of how atmospheric acoustic waves interact with the solid Earth.

Seismic Deployments

Embayment Seismic Excitation Experiment (ESEE)
Non-Volcanic Tremor Array (NVTA)
Small Experiments in the Embayment
Northern Embayment Lithosphere Experiment (NELE)
IRIS Wavefields Community Experiment (YW)
Magseis Fairfield Nodal Seismometer Facility at CERI

Wave Gradiometry, Strain, and Rotation

Wave Gradiometry
Plate Boundary Observatory GTSM Calibration

Continuous Wavelet Transform Denoising and Processing

Theory
Software

Acoustic-Seismic

4 November 2003 Bolide over Northeastern Arkansas
Thunder Seismology - Moscow Acoustic Seismic Array (MASA)
Induced Earthquakes - The Greenbrier Array
Response of the Mississippi Embayment from Space Shuttle N Waves