Determination of earthquake moment tensors from teleseismic relative amplitude observations

Pearce, Robert G.; Rogers, Richard M.

doi:10.1029/jb094ib01p00775

Cited by 36 publications

(17 citation statements)

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“…These echoes can preferentially be pP and sP phases, and as was shown by Pearce & Rogers (1989), a teleseismic signal is mainly dominated by the three phase arrivals of P waves, pP and sP. This can also be extended, for instance, to pP and PcP phase detection, or other converted/reflected phases that are not linked to the free surface (e.g.…”

Section: New Cepstral Definition Using Three Phase Arrivals (Two Echoes)mentioning

confidence: 97%

A new, improved and fully automatic method for teleseismic depth estimation of moderate earthquakes (4.5 < M < 5.5): application to the Guerrero subduction zone (Mexico)

Letort

Guilbert

Cotton

et al. 2015

Geophysical Journal International

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: A new, improved and fully automatic method for teleseismic depth estimation of moderate earthquakes (4.5 < M < 5.5): application to the Guerrero subduction zone (Mexico). -Geophysical Journal International, 201, p. 1834-1848 • ) through the study of the spectral holes in the shape of the signal spectrum. The ability of our automatic method to improve depth estimations is shown by relocation of the recent moderate seismicity of the Guerrero subduction area (Mexico). We have therefore estimated the depth of 152 events using teleseismic data from the IRIS stations and arrays. One advantage of this method is that it can be applied for single stations (from IRIS) as well as for classical arrays. In the Guerrero area, our new cepstral analysis efficiently clusters event locations and provides an improved view of the geometry of the subduction. Moreover, we have also validated our method through relocation of the same events using the new International Seismological Centre (ISC)-locator algorithm, as well as comparing our cepstral depths with the available Harvard-Centroid Moment Tensor (CMT) solutions and the three available ground thrust (GT5) events (where lateral localization is assumed to be well constrained with uncertainty <5 km) for this area. These comparisons indicate an overestimation of focal depths in the ISC catalogue for deeper parts of the subduction, and they show a systematic bias between the estimated cepstral depths and the ISC-locator depths. Using information from the CMT catalogue relating to the predominant focal mechanism for this area, this bias can be explained as a misidentification of sP phases by pP phases, which shows the greater interest for the use of this new automatic cepstral analysis, as it is less sensitive to phase identification.

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Section: New Cepstral Definition Using Three Phase Arrivals (Two Echoes)mentioning

confidence: 97%

A new, improved and fully automatic method for teleseismic depth estimation of moderate earthquakes (4.5 < M < 5.5): application to the Guerrero subduction zone (Mexico)

Letort

Guilbert

Cotton

et al. 2015

Geophysical Journal International

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“…We suspect that the anomalous nature of the BB waveform at YSS may be due to a receiver effect, and/or errors in the specification of the instrument response used to convert the original data to BB displacement. Moment tensor analysis We use the relative amplitude method (PEARCE 1977(PEARCE , 1980PEARCE and ROGERS, 1989) to find moment tensors that are consistent with the observed SP and BB P waveforms. The method compares synthetic relative amplitude ratios of pP =P , sP =P , and sP =pP , calculated for a second-order moment tensor, with those observed.…”

Section: Figurementioning

confidence: 98%

“…The six independent variables of the moment tensor can be expressed as two source-type parameters (T [À1:0, 1.0] the deviatoric part, and k [À1:0, 1.0] the volumetric part), three orientation parameters (r [0 , 360 ], d [0 , 180 ] and w [0 , 180 ]), and the scalar moment M 0 (HUDSON et al, 1989;PEARCE and ROGERS, 1989). Since we use relative amplitudes we cannot determine M 0 .…”

Section: Figurementioning

confidence: 99%

Discriminating Between Large Mine Collapses and Explosions Using Teleseismic P Waves

Bowers¹

2002

Pure and Applied Geophysics

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Some of the most suspicious seismic disturbances under the Comprehensive Nuclear-Test-Ban Treaty (CTBT) are likely to be those associated with mining, as they are shallow, and at least some have an explosion-like m b :M s signature. Previous research highlighted the potential of broadband teleseismic P waves as a way of identifying large mine tremors. Broadband teleseismic P from two suspected large mine collapses, one in Germany (1302 UT, 13 March 1989 ) and another in Wyoming (1526 UT, 3 February 1995, 5.3 m b ), show differences in character despite the similarity of the reported ground failure and mine types. We apply a full moment-tensor analysis to the teleseismic P waves and show that the data are inconsistent with either a shallow explosion or an earthquake (double-couple) at depth, but this method is unable to distinguish between a shallow dip-slip source and a closing-crack moment tensor. However, three-component surface-wave seismograms recorded at regional distances fit the shallow closing-crack model, but are inconsistent with a shallow earthquake source, because strong Love waves, expected from a double-couple source, are not observed at a number of stations well distributed in azimuth. Here, we restate the equivalence for shallow sources of the closing-crack model and a gravitational collapse model. We use the latter to model the broadband P waves from these mine tremors and show that, while non-unique, the differences in the observed broadband P waves from the two tremors can be attributed to the area, amount of collapse, depth, and rate of collapse. The collapse model predicts negative first-motion for all P waves in contrast to the positive polarity expected from explosions. Thus, the broadband teleseismic P waves have the potential to discriminate between large collapses and explosions.Pure and Applied Geophysics is desirable to minimise the number of unnecessary on-site inspections or ''false alarms.'' BOWERS and DOUGLAS (1997) analysed short-period (SP) and broadband (BB) teleseismic P seismograms from seismic disturbances in many mining regions, and noted that in general the SP P waves are simple (having a short-duration pulse with little or no coda), with negative (dilatational) first-motion. Further, BOWERS and DOUGLAS (1997) showed that even where the SP first-motion was unclear, the BB P onset generally has a clear negative first-motion. BOWERS and DOUGLAS (1997) concluded that the first motion of BB teleseismic P has the potential to discriminate between shallow mine tremors and explosions (as the BB P first-motion from an explosion is expected to be positive). However, the physical basis for the BB teleseismic P discriminant is still not understood fully. BOWERS (1997) showed that negative-polarity teleseismic P waves and threecomponent surface waves from a large mine tremor, on 30 October 1994, in the Welkom district of South Africa, are best explained by a double-couple moment tensor at a depth of 2.3 km. However, it is well established that not all mine tremors are due to shallow do...

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“…If then, simple seismograms are recorded over a wide range of distance and particularly azimuth, it is unlikely the source is an earthquake at depth. It is possible to test this with the method of Pearce (Barley and Pearce 1977;Pearce 1977Pearce , 1980Pearce and Rogers 1989;Pearce 1996) originally developed to determine focal mechanisms of earthquakes from the relative amplitudes of direct P and the surface reflections. For source identification the procedure is to use only the simple P seismograms on the assumption that whereas the propagation through Earth may make a signal more complex it is unlikely to make it simpler.…”

Section: Using Seismogram Modelling To Understand Discriminationmentioning

confidence: 99%

Forensic seismology revisited

Douglas

2007

Surv Geophys

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The first technical discussions, held in 1958, on methods of verifying compliance with a treaty banning nuclear explosions, concluded that a monitoring system could be set up to detect and identify such explosions anywhere except underground: the difficulty with underground explosions was that there would be some earthquakes that could not be distinguished from an explosion. The development of adequate ways of discriminating between earthquakes and underground explosions proved to be difficult so that only in 1996 was a Comprehensive Nuclear Test Ban Treaty (CTBT) finally negotiated. Some of the important improvements in the detection and identification of underground teststhat is in forensic seismology-have been made by the UK through a research group at the Atomic Weapons Establishment (AWE). The paper describes some of the advances made in identification since 1958, particularly by the AWE Group, and the main features of the International Monitoring System (IMS), being set up to verify the Test Ban.Once the Treaty enters into force, then should a suspicious disturbance be detected the State under suspicion of testing will have to demonstrate that the disturbance was not a test. If this cannot be done satisfactorily the Treaty has provisions for on-site inspections (OSIs): for a suspicious seismic disturbance for example, an international team of inspectors will search the area around the estimated epicentre of the disturbance for evidence that a nuclear test really took place.Early observations made at epicentral distances out to 2,000 km from the Nevada Test Site showed that there is little to distinguish explosion seismograms from those of nearby earthquakes: for both source types the short-period (SP: *1 Hz) seismograms are complex showing multiple arrivals. At long range, say 3,000-10,000 km, loosely called teleseismic distances, the AWE Group noted that SP P waves-the most widely and well-recorded waves from underground explosions-were in contrast simple, comprising one or two cycles of large amplitude followed by a low-amplitude coda. Earthquake signals on the other hand were often complex with numerous arrivals of similar amplitude spread over 35 s or more. It therefore appeared that earthquakes could be recognised on complexity.Later however, complex explosion signals were observed which reduced the apparent effectiveness of complexity as a criterion for identifying earthquakes. Nevertheless, the AWE Group concluded that for many paths to teleseismic distances, Earth is transparent for P signals and this provides a window through which source differences will be most clearly seen. Much of the research by the Group has focused on understanding the influence of source type on P seismograms recorded at teleseismic distances. Consequently the paper concentrates on teleseismic methods of distinguishing between explosions and earthquakes.One of the most robust criteria for discriminating between earthquakes and explosions is the m b : M s criterion which compares the amplitudes of the SP P waves as measured ...

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Determination of earthquake moment tensors from teleseismic relative amplitude observations

Cited by 36 publications

References 20 publications

A new, improved and fully automatic method for teleseismic depth estimation of moderate earthquakes (4.5 < M < 5.5): application to the Guerrero subduction zone (Mexico)

A new, improved and fully automatic method for teleseismic depth estimation of moderate earthquakes (4.5 < M < 5.5): application to the Guerrero subduction zone (Mexico)

Discriminating Between Large Mine Collapses and Explosions Using Teleseismic P Waves

Forensic seismology revisited

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