Improving local earthquake locations using the L1 norm and waveform cross correlation: Application to the Whittier Narrows, California, aftershock sequence

Shearer, Peter M.

doi:10.1029/96jb03228

Cited by 318 publications

(239 citation statements)

References 52 publications

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“…This was illustrated by the invariant size of the half axes of the error ellipsoids. Their effects on hypocenter locations are, however, not negligible and could be comparable to studies on effects of mispicks on earthquake location (Shearer, 1997).…”

Section: Discussionsupporting

confidence: 50%

Detection of Systematic Errors in Travel-Time Data Using a Minimum 1D Model: Application to Costa Rica Seismic Tomography

Maurer¹,

Kissling²,

Husen³

et al. 2010

Bulletin of the Seismological Society of America

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Many seismological studies depend on the accuracy of timing of seismological data. In seismic tomography, travel-time residuals defined as differences between the observed and calculated arrival times of seismic phases are minimized to constrain 3D velocity structure. Inconsistencies and large errors in data sets that result from incorrect station coordinates, errors in the timing acquisition system, errors in the merging procedure, inconsistency in the picking and phase misidentification can also generate travel-time residuals, and because of their systematic nature, these errors cannot be treated as random noise even by exploiting a large number of travel times. While the inverse problem is perfectly set up to deal with random noise, systematic errors lead to significant artifacts in the solution, but may not be detected by a posterior error assessment. For this reason, detecting and removing systematic travel-time errors from data sets before inversion is crucial for seismic tomography studies.We present a methodology based on the use of a minimum 1D model to detect and remove systematic errors in travel-time data by detailed analysis of station delays and observation residuals and apply it to a local earthquake data set from Costa Rica. The determination of the exact nature of detected inconsistencies needs further investigations in each individual case. If the cause of detected systematic errors cannot be determined beyond any doubt and the afflicted data may not be corrected, they must be deleted from the data set. To assess the extent of influence of systematic errors on hypocenter locations and their uncertainties, we present two examples showing the effects of station mislocation.

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Section: Discussionsupporting

confidence: 50%

Detection of Systematic Errors in Travel-Time Data Using a Minimum 1D Model: Application to Costa Rica Seismic Tomography

Maurer¹,

Kissling²,

Husen³

et al. 2010

Bulletin of the Seismological Society of America

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“…Differential travel times from waveform cross correlation (WCC) can also be included in the procedure allowing further constraints to be put in the inversion. These differential travel times are included as additional information to the observed arrival times in order to solve for a new set of adjusted picks by minimizing the misfit of both the original picks and the differential times (Shearer, 1997). This procedure requires a similar-event cluster identification and is termed by Shearer et al (2005) as cluster analysis.…”

Section: Earthquake Relocationmentioning

confidence: 99%

“…Most of the aftershocks have hypocentral depths comparable to the mainshock and in the range between 15 and 25 km. We estimate uncertainties for these relative locations using a bootstrap technique where random errors (drawn from a normal distribution) are added to the picks and each event is relocated 200 times (see Shearer, 1997;Evangelidis et al, 2008). This procedure will result in a cloud of locations for whose horizontal and vertical scatter can be used in order to estimate errors.…”

Section: Earthquake Relocationmentioning

confidence: 99%

Rupture Process and Aftershocks Relocation of the 8 June 2008 Mw 6.4 Earthquake in Northwest Peloponnese, Western Greece

Konstantinou¹,

Melis²,

Lee³

et al. 2009

Bulletin of the Seismological Society of America

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On 8 June 2008 at 12:25 (GMT) an M w 6.4 strong earthquake occurred in the area of northwest Peloponnese, western Greece, causing the death of two people and extensive damage to the surrounding area. The main event and its aftershocks were recorded by one nationwide and three regional networks equipped with threecomponent broadband seismometers. Initial locations of the earthquake sequence comprising 438 aftershocks showed a linear northeast-southwest trend and that the mainshock was located at 22 km depth. After the relocation using catalog and differential travel times, most events form three distinct clusters at depths 15-25 km. Moment tensor solutions for the main event and its largest aftershocks exhibited a pure strike-slip mechanism with one nodal plane orientated northeast-southwest in accordance with the relocated seismicity. A parallel, nonnegative least-squares inversion technique utilizing multiple-time windows was used to derive the spatiotemporal slip distribution of the main event. The resulting slip distribution model revealed a large slip patch (maximum slip ∼150 cm) between 10 and 20 km depth at the northeast part of the fault that also coincides with the area that suffered most of the damage. Another patch exhibiting smaller amounts of slip (20-50 cm) is located to the southwest direction at the same depth range, and smaller patches exist at 25-30 km depth. Most aftershocks are located in areas of low slip (< 25 cm) filling the regions of slip deficit. The 8 June earthquake occurred at an area where no previous seismological or other observations indicated the existence of a seismogenic fault at that depth and with this strike. This, and the fact that the event nucleated in the middle to lower crust, may be interpreted as the reactivation of a fault structure that was inherited from previous tectonic phases.Online Material: Spatiotemporal evolution of the aftershock sequence of the 8 June 2008 mainshock, sensitivity tests to the mainshock slip inversion, color versions of figures, relocated aftershocks catalog, classification scheme for the moment tensor solutions, and moment tensor inversion description.

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“…There are usually advantages of using the so-called L1 norm (Shearer 1997), although the procedure described here to calculate slowness corrections is more tractable using the L2 norm. The actual location calculations, with or without slowness corrections, can be solved using either L1 or L2 norm minimization.…”

Section: Calculating Empirical Slowness Correctionsmentioning

confidence: 99%

Accurate relative location estimates for the North Korean nuclear tests using empirical slowness corrections

Gibbons¹,

Pabian

Näsholm³

et al. 2016

Geophys. J. Int.

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SUMMARYDeclared North Korean nuclear tests in 2006, 2009, 2013, and 2016 were observed seismically at regional and teleseismic distances. Waveform similarity allows the events to be located relatively with far greater accuracy than the absolute locations can be determined from seismic data alone. There is now significant redundancy in the data given the large number of regional and teleseismic stations that have recorded multiple events, and relative location estimates can be confirmed independently by performing calculations on many mutually exclusive sets of measurements. Using a 1-dimensional global velocity model, the distances between the events estimated using teleseismic P phases are found to be approximately 25% shorter than the distances between events estimated using regional Pn phases. The 2009The , 2013, and 2016 events all take place within 1 km of each other and the discrepancy between the regional and teleseismic relative location estimates is no more than about 150 m. The discrepancy is much more significant when estimating the location of the more distant 2006 event relative to the later explosions with regional and teleseismic estimates varying by many hundreds of meters. The relative location of the 2006 event is challenging given the smaller number of observing stations, the lower signal-to-noise ratio, and significant waveform dissimilarity at some regional 2 S. J. Gibbons et al.stations. The 2006 event is however highly significant in constraining the absolute locations in the terrain at the Punggye-ri test-site in relation to observed surface infrastructure.For each seismic arrival used to estimate the relative locations, we define a slowness scaling factor which multiplies the gradient of seismic traveltime versus distance, evaluated at the source, relative to the applied 1-d velocity model. A procedure for estimating correction terms which reduce the double-difference time residual vector norms is presented together with a discussion of the associated uncertainty. The modified velocity gradients reduce the residuals, the relative location uncertainties, and the sensitivity to the combination of stations used. The traveltime gradients appear to be overestimated for the regional phases, and teleseismic relative location estimates are likely to be more accurate despite an apparent lower precision. Calibrations for regional phases are essential given that smaller magnitude events are likely not to be recorded teleseismically. We discuss

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Improving local earthquake locations using the L1 norm and waveform cross correlation: Application to the Whittier Narrows, California, aftershock sequence

Cited by 318 publications

References 52 publications

Detection of Systematic Errors in Travel-Time Data Using a Minimum 1D Model: Application to Costa Rica Seismic Tomography

Detection of Systematic Errors in Travel-Time Data Using a Minimum 1D Model: Application to Costa Rica Seismic Tomography

Rupture Process and Aftershocks Relocation of the 8 June 2008 Mw 6.4 Earthquake in Northwest Peloponnese, Western Greece

Accurate relative location estimates for the North Korean nuclear tests using empirical slowness corrections

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