Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Billings, S. D. Articles by Kennett, B. L. N. Search for Related Content GeoRef GeoRef Citation

Errors in hypocenter location: Picking, model, and magnitude dependence

Research School of Earth Sciences Institute of Advanced Studies Australian National University, Canberra, Australia

Abstract

The location procedures of seismic events are influenced by two major classes of errors, the error in picking individual seismic phases and modeling error due to the departure of the real Earth from the reference model used in the location. Both classes of error influence the estimate of location and it is difficult to separate them.

The role of picking errors can be assessed by a nonlinear analysis using a Monte Carlo procedure. Arrivals times are perturbed with random numbers drawn from a normal distribution, and the event is relocated using these perturbed arrival times. By repeating the procedure many times, a cluster of locations is obtained, which can be used to investigate the effects of picking errors on the hypocenter. This analysis is insensitive to velocity-model errors as these are fixed for a given combination of stations and phases. Some care must be exercised when analysing multidimensional distributions in two-dimensional slices because of a projection effect.

The modeling error due to the influence of lateral heterogeneity in the Earth is examined by comparing the locations of the same event using different combinations of phases and network geometries, which reinforces the need to use arrivals other than P for accurate depth resolution. The sensitivity of P arrivals to changes in depth are swamped by model errors, and inclusion of depth-sensitive phases such as pP is highly recommended. The effect of picking errors on location is found to be much smaller than the mislocation caused by neglecting lateral heterogeneity when only P arrivals are used. Consequently, the Monte Carlo analysis, which is primarily aimed at picking errors only, is most appropriate when multiple phases have been used to more accurately constrain the hypocenter, especially for the depth component.

Altering the type of phase data used in the location plays a similar role in changing the network geometry, in that both are mechanisms that influence the nature of the constraint on the hypocenter. By relocating events with network geometries corresponding to the different magnitudes, it is found that the location of the event can be affected significantly by the magnitude, and when using robust statistics to describe earthquake residuals, the mislocation can occur in a systematic manner. The effect is marked in regions with significant lateral variations in seismic velocities. For example, low-magnitude events in the Flores Sea are found to be dragged toward Australia as a result of the fast paths to Australian stations relative to the iasp91 reference velocity model.

This article has been cited by other articles:

				I. Bondar and K. McLaughlin Seismic Location Bias and Uncertainty in the Presence of Correlated and Non-Gaussian Travel-Time Errors Bulletin of the Seismological Society of America, February 1, 2009; 99(1): 172 - 193. [Abstract] [Full Text] [PDF]

				J. J. McGuire Seismic Cycles and Earthquake Predictability on East Pacific Rise Transform Faults Bulletin of the Seismological Society of America, June 1, 2008; 98(3): 1067 - 1084. [Abstract] [Full Text] [PDF]

				C. P. Evangelidis, K. I. Konstantinou, N. S. Melis, M. Charalambakis, and G. N. Stavrakakis Waveform Relocation and Focal Mechanism Analysis of an Earthquake Swarm in Trichonis Lake, Western Greece Bulletin of the Seismological Society of America, April 1, 2008; 98(2): 804 - 811. [Abstract] [Full Text] [PDF]

				J. Schweitzer and B. L. N. Kennett Comparison of Location Procedures: The Kara Sea Event of 16 August 1997 Bulletin of the Seismological Society of America, April 1, 2007; 97(2): 389 - 400. [Abstract] [Full Text] [PDF]

				A. Douglas, J. B. Young, D. Bowers, and P. D. Marshall An Analysis of P Travel Times for Nevada Test Site Explosions Recorded at Regional Distances Bulletin of the Seismological Society of America, June 1, 2005; 95(3): 941 - 950. [Abstract] [Full Text] [PDF]

				S. C. Myers Reply to "Comment on 'Improving Sparse Network Seismic Location with Bayesian Kriging and Teleseismically Constrained Calibration Events,' by Stephen C. Myers and Craig A. Schultz," by A. Douglas Bulletin of the Seismological Society of America, February 1, 2005; 95(1): 370 - 372. [Full Text] [PDF]

				Validation of Regional and Teleseismic Travel-Time Models by Relocating Ground-Truth Events Bulletin of the Seismological Society of America, June 1, 2004; 94(3): 897 - 919.

				Earthquake Locations in the Inner Continental Borderland, Offshore Southern California Bulletin of the Seismological Society of America, April 1, 2000; 90(2): 425 - 449.

				Optimal Seismic Networks in Israel in the Context of the Comprehensive Test Ban Treaty Bulletin of the Seismological Society of America, February 1, 2000; 90(1): 151 - 165.

				Improving Sparse Network Seismic Location with Bayesian Kriging and Teleseismically Constrained Calibration Events Bulletin of the Seismological Society of America, February 1, 2000; 90(1): 199 - 211.

				B. R. Lienert Assessment of earthquake location accuracy and confidence region estimates using known nuclear tests Bulletin of the Seismological Society of America, October 1, 1997; 87(5): 1150 - 1157. [Abstract] [PDF]

				C. Lomnitz Comment on "Errors in hypocenter location: Picking, model, and magnitude dependence," by S. D. Billings, M. S. Sambridge, and B. L. N. Kennett Bulletin of the Seismological Society of America, October 1, 1995; 85(5): 1527 - 1528. [PDF]

				S. D. Billings, M. S. Sambridge, and B. L. N. Kennett Reply to comment on "Errors in hypocenter location: Picking, model, and magnitude dependence" by C. Lomnitz Bulletin of the Seismological Society of America, October 1, 1995; 85(5): 1529 - 1529. [PDF]