Short-period Lg magnitudes: Instrument, attenuation, and source effects

1983 ◽  
Vol 73 (6A) ◽  
pp. 1835-1850
Author(s):  
Robert B. Herrmann ◽  
Andrzej Kijko
Keyword(s):  
United States ◽  
Epicentral Distance ◽  
P Wave ◽  
Magnitude Scale ◽  
Source Effects ◽  
Anelastic Attenuation ◽  
Basic Conclusion ◽  
Short Period ◽  
Central United States ◽  
Definition Of

Abstract The applicaton of the Nutli (1973) definition of the mbLg magnitude to instruments and wave periods other than the short-period WWSSN seismograph is examined. The basic conclusion is that the Nuttli (1973) definition is applicable to a wider range of seismic instruments if the log10(A/T) term is replaced by log10A. For consistency and precision, the notation mbLg should be applied only to magnitudes based upon 1.0 Hz observations. The mbLg magnitude definition was constrained to be consistent with teleseismic P-wave mb estimates from four Central United States earthquakes. In general, for measurements made at a frequency f, the notation mLg(f) should be used, where m L g ( f ) = 2.94 + 0.833 log ⁡ 10 ( r / 10 ) + 0.4342 γ r + log ⁡ 10 A , and r is the epicentral distance in kilometers, γ is the coefficient of anelastic attenuation, and A is the reduced ground amplitude in microns. Given its stability when estimated from different instruments, the mLg(f) magnitude is an optimum choice for an easily applied, standard magnitude scale for use in regional seismic studies.

Spatial attenuation of intensities for central U.S. earthquakes

1976 ◽  
Vol 66 (3) ◽  
pp. 743-751
Author(s):  
Indra N. Gupta ◽  
Otto W. Nuttli
Keyword(s):  
United States ◽  
Ground Motion ◽  
Epicentral Distance ◽  
Near Field ◽  
Mississippi Valley ◽  
Average Value ◽  
Anelastic Attenuation ◽  
Central United States ◽  
Using Data ◽  
Spatial Attenuation

abstract Attenuation of ground motion in the central United States has to be determined principally using the Modified Mercalli (MM) intensity observations because of the absence of instrumental strong ground-motion data. Nuttli's previous studies of Mississippi Valley earthquakes indicate that higher-mode surface waves produce the largest ground motion except possibly in the near-field region. Particle velocity rather than acceleration correlates directly with intensity and the coefficient of anelastic attenuation has an average value of 0.10 per degree. Using data from isoseismals of the November 9, 1968, southern Illinois and the December 16, 1811, New Madrid, Missouri earthquakes and assuming a linear relationship between log(A/T) and MM intensity, attenuation is expressed by the equation, valid for I(R) ≧IV (MM), I ( R ) = I 0 + 3.7 − 0.0011 R − 2.7 log ⁡ R ; for R ≧ 20 k m where R is the epicentral distance in kilometers. This relationship shows fairly good agreement with isoseismals of many large earthquakes in the central United States and may therefore be useful in providing realistic estimates of spatial attenuation and hence of design earthquakes for a given site. It can also be sometimes useful in estimating the epicentral intensity of an earthquake whose maximum intensity is not reliably known.

Short-period P-wave attenuation along various paths in North America as determined from P-wave spectra of the SALMON nuclear explosion

1976 ◽  
Vol 66 (5) ◽  
pp. 1609-1622 ◽  
Author(s):  
Zoltan A. Der ◽  
Thomas W. McElfresh
Keyword(s):  
United States ◽  
North America ◽  
Wave Attenuation ◽  
Nuclear Explosion ◽  
P Wave ◽  
Western United States ◽  
Source Spectrum ◽  
Wave Spectra ◽  
Short Period ◽  
Q Values

abstract Average Q values were determined for ray paths to various LRSM stations from the SALMON nuclear explosion by taking ratios of observed P-wave spectra to the estimated source spectrum. Most Q values for P-wave paths throughout eastern North America are in the range 1600 to 2000 while those crossing over into the western United States are typically around 400 to 500. These differences in Q for intermediate distances can sufficiently explain the differences in the teleseismic event magnitudes observed, 0.3 to 0.4 magnitude units, in the western versus the eastern United States, if one assumes that the low Q layer under the western United States is located at depths less than 200 km.

Local Richter magnitude and total signal duration in southern California

1973 ◽  
Vol 63 (5) ◽  
pp. 1809-1827 ◽  
Author(s):  
Charles R. Real ◽  
Ta-Liang Teng
Keyword(s):  
Southern California ◽  
Epicentral Distance ◽  
Total Duration ◽  
Signal Duration ◽  
Local Magnitude ◽  
Total Signal ◽  
Source Effects ◽  
Short Period ◽  
Seismic Networks ◽  
Southern California Region

abstract Seismograms of 320 earthquakes (1,486 observations) from short-period seismometers occurring from January 1969 to April 1971 and 91 earthquakes (257 observations) during 1971 have been used to establish a relationship between total signal duration and the local Richter magnitude for the CIT and BHSN telemetered seismic networks in southern California. The data have been fitted using regression analysis to relationships of the form M τ = C 0 + C 1 log ⁡ τ + C 2 Δ M τ ≦ 3.8 M τ = C 0 + C 1 ( log ⁡ τ ) 2 + C 2 Δ M τ > 3.8 where τ is the total duration in seconds and Δ is the epicentral distance in kilometers. These relations explain up to 88 per cent (CIT) and 94 per cent (BHSN) of the variation in the data and yield magnitudes having standard deviations as low as 0.15 (CIT) and 0.14 (BHSN) magnitude units. It has been found that the local magnitude based on signal duration is relatively insensitive to variations in azimuth and source effects. In view of the limited distribution and low magnifiation of the Wood-Anderson torsion seismometer, and the previously recognized problems of “saturation” and instrument response associated with the amplitude technique, it is concluded that the method of duration applied to vertical short-period seismograph records will greatly improve the assignment of local magnitude to earthquakes in the southern California region.

scholarly journals Drought Variability and Trends over the Central United States in the Instrumental Record

2018 ◽  
Vol 19 (7) ◽  
pp. 1149-1166 ◽  
Author(s):  
Kingtse C. Mo ◽  
Dennis P. Lettenmaier
Keyword(s):  
United States ◽  
Land Surface ◽  
Land Surface Models ◽  
Drought Variability ◽  
The North ◽  
Surface Models ◽  
Central United States ◽  
Uniform Probability Distribution ◽  
Sea Surface Temperature Anomalies ◽  
Definition Of

Abstract We examined drought variability and trends over the last century (1916–2013) over the conterminous United States (CONUS) using observed precipitation P, temperature T, and reconstructed total moisture percentiles (TMP) and runoff from four land surface models. We used an integrated drought index (IDI), which we defined as the equally weighted mean of the 3-month standardized runoff index (SRI3) and TMP from four land surface models mapped onto a uniform probability distribution. Using a definition of drought as IDI less than 0.3 for 6 months or longer, we identified 16 drought events, which we termed great droughts that covered more than 50% of the CONUS during our study period. We examined the properties of great droughts and compared these with the 2012 event. The great droughts were located at least partially over the central United States (30°–42°N, 85°–110°W). We found that 12 of these great droughts occurred when cold sea surface temperature anomalies (SSTAs) were located in the tropical Pacific with warm SSTAs in the North Atlantic. We also found a predominance of decreasing trends in IDI; droughts occurred less often and events were less severe as time progressed. In particular, only 2 of the 16 great droughts (2012 and 1988) occurred in the second half of the record.

A discrimination analysis of short-period regional seismic data recorded at Tonto Forest Observatory

1982 ◽  
Vol 72 (4) ◽  
pp. 1351-1366
Author(s):  
J. R. Murphy ◽  
T. J. Bennett
Keyword(s):  
Epicentral Distance ◽  
Test Site ◽  
P Wave ◽  
Set Cover ◽  
Spectral Amplitude ◽  
Nevada Test Site ◽  
Data Set ◽  
Short Period ◽  
Single Station ◽  
Regional Phases

abstract A new seismic discriminant based on spectral differences of regional phases from earthquakes and explosions recorded at a single station has been tested and found to work remarkably well. The test data consisted of a well-constrained set of 30 Nevada Test Site (NTS) explosions and 21 earthquakes located within about 100 km of NTS which were recorded on short-period seismographs at the Tonto Forest Observatory in central Arizona at an epicentral distance averaging 530 km. The events in the data set cover a magnitude range from 3.3 to 4.8 (mb) for which Pn, Pg, and Lg phases have been analyzed. We found that, although Lg phases from earthquakes are typically more prominent than for explosions with comparable P-wave amplitude levels, simple time-domain Lg/P amplitude ratios do not result in a separation of the earthquake and explosion samples consistent enough to provide reliable discrimination. However, spectral analyses of the data over the frequency band from 0.5 to 5.0 Hz revealed significant differences in the spectra of certain regional phases which proved to be a quite reliable discriminant. In particular, both the Pg and Lg spectra from earthquakes have been found to be richer in high-frequency content than corresponding explosion spectra. A discriminant measure, defined as the ratio of average Lg spectral amplitude level in the 0.5- to 1.0-Hz passband to that in the 2.0- to 4.0-Hz passband, provides good separation of earthquake and explosion populations.

An amplitude constrained P-wave velocity profile for the upper mantle beneath the Eastern United States

1979 ◽  
Vol 69 (6) ◽  
pp. 1733-1744
Author(s):  
George A. McMechan
Keyword(s):  
United States ◽  
Velocity Profile ◽  
Wave Velocity ◽  
Upper Mantle ◽  
Epicentral Distance ◽  
P Wave ◽  
Eastern United States ◽  
Lateral Velocity ◽  
The North ◽  
P Wave Velocity

abstract A P-wave velocity profile for the upper mantle at depths between 200 and 800 km beneath Eastern United States has been constructed from a combination of data from natural and artificial sources. Data for this part of the upper mantle are scarce, particularly beyond 20° epicentral distance, because of the sparse distribution of relevant sources and stations. Nevertheless, this study is the first to use amplitude constraints in a model determination for this region, and the model that has been chosen can account for the main observed amplitude features as well as travel times. The resulting velocity profile is similar to those previously determined for the regions to the north and west, but has a broadening of velocity transitions relative to those in the western United States. Evidence is found for the existence of lateral velocity inhomogeneity within the mantle.

scholarly journals Regional variations in the structure of the crust in the central United States from P-wave spectra

1973 ◽  
Vol 63 (5) ◽  
pp. 1663-1687
Author(s):  
Tuneto Kurita
Keyword(s):  
United States ◽  
Gulf Of Mexico ◽  
Crustal Structure ◽  
Coastal Plain ◽  
Lower Crust ◽  
P Wave ◽  
Ratio Method ◽  
Gulf Coastal Plain ◽  
Regional Variations ◽  
Central United States

abstract Regional variations in the crustal structure in the central United States have been inferred by the transfer ratio method from an analysis of long-period P waves recorded at SHA, OXF, FLO and MDS, the stations nearly along 89°W longitude. The crustal structure in this region is approximated by a stack of horizontal parallel layers except possibly in the area around FLO, where the structure is rather complicated. The crustal thickness is predominantly controlled by the thick silicic upper crust, whereas the mafic lower crust is about 10 km thick throughout this region. The P-wave velocity of the lower crust is about 6.9 to 7.0 km/sec except probably in the area around FLO, where 7.4 km/sec velocity is more likely. A sedimentary layer with a velocity of about 3.0 km/sec, having a thickness of about 3 km near the coast of the Gulf of Mexico, tapers out to the north within the Gulf Coastal Plain. Deep discontinuities in the crust may be replaced by transitional layers up to 10 km thick. The Moho is about 33 km deep near the coast of the Gulf of Mexico, deepens to about 41 km near an intersection of the Gulf coastal plain and the interior plain, reaches about 47 km or more in the midst of the interior plain, and rises to about 41 km toward an intersection of the interior plain and the superior upland. As for the midst of the interior plain, however, the depth of the Moho reduces by as much as 5 km, if the velocity in the lower crust is about 7.0 km/sec instead of about 7.4 km/sec. In any case, the general trend of the depth of the Moho may match with the topographic feature from the Gulf of Mexico to Lake Superior.

Seismicity of the southeastern United States

1973 ◽  
Vol 63 (5) ◽  
pp. 1785-1808
Author(s):  
G. A. Bollinger
Keyword(s):  
United States ◽  
South Carolina ◽  
Southeastern United States ◽  
Vertical Component ◽  
Seismic Zone ◽  
Local Magnitude ◽  
Short Period ◽  
Central United States ◽  
Order Of Magnitude ◽  
Attenuation Characteristics

abstract Review and analysis of the existing data base for southeastern United States earthquakes indicate that the spatial pattern of energy release can be interpreted to occur in zones both parallel (southern Appalachian seismic zone) and transverse (central Virginia and South Carolina-Georgia seismic zones) to the regional Appalachian structural trend. The temporal pattern, for events V ≦ Io ≦ VIII, can be expressed by the recursion relationship, log N = 3.01 − 0.59 Io. Felt areas are, in general, one order of magnitude greater than for similar west coast events. Their configuration is elliptical and aligned with regional structure, except in central Virginia and Alabama and in coastal South Carolina. These latter areas have circular or lobate felt areas that may be caused by differences in focal depths and/or focal mechanisms. A tentative local magnitude formula is developed that employs the vertical component of the short-period Lg phase. It appears that the regional attenuation characteristics of this phase are similar to those found by Nuttli (1973a) in the central United States.

Upper mantle P-wave model catalogue

1976 ◽  
Vol 13 (10) ◽  
pp. 1481-1486 ◽  
Author(s):  
George A. McMechan ◽  
Judith J. Sinclair
Keyword(s):  
Upper Mantle ◽  
Epicentral Distance ◽  
Vertical Component ◽  
Wave Model ◽  
Synthetic Seismograms ◽  
P Wave ◽  
P Wave Velocity ◽  
Short Period ◽  
Distance Travel ◽  
Ray Parameter

This note is a description of a catalogue that contains tables of parameters and synthetic seismograms for 50 upper-mantle P-wave velocity–depth profiles. The table for each model contains values of ray parameter, epicentral distance, travel time, velocity, and bottoming depth for a number of representative rays. Short-period synthetic seismograms are computed at 1 °intervals from 10° to 30° by the quantized ray theory algorithm and are vertical component traces for a surface focus point source. The catalogue is designed as a comprehensive reference and so includes a wide variety of mantle models.

Attenuation of regional phases in Western Europe

1982 ◽  
Vol 72 (6A) ◽  
pp. 2089-2106
Author(s):  
Marc Nicolas ◽  
Bernard Massinon ◽  
Pierre Mechler ◽  
Michel Bouchon
Keyword(s):  
United States ◽  
Western Europe ◽  
Eastern United States ◽  
Large Scatter ◽  
The Caspian Sea ◽  
Attenuation Coefficients ◽  
Anelastic Attenuation ◽  
Short Period ◽  
Regional Phases ◽  
Mean Trend

abstract The purpose of this study is to evaluate the attenuation of local seismic phases in France. We use the 25 short-period vertical stations of the French seismic network and select a set of six earthquakes which occurred in France or in its vicinity, and within a range of epicentral distances from 1° to 10°. We have determined the attenuation versus distance for Pn, Sn, Pg, and Lg phases and analyzed the influence of frequency. Attenuation coefficients for Pn and Sn waves are of the order of 2. They are slightly higher for Pg (2.3) and Lg (2.5) waves, but the amplitude of these waves is largely dependent on the azimuth of propagation. Lg/Pg ratios present a large scatter between 1 and 10 with a mean trend around 3 to 4. We found that the Lg anelastic attenuation coefficient is of the order of 0.2 deg−1 at 1 Hz, a result to be compared with the values of 0.07 deg−1 (Eastern United States), 0.15 deg−1 (Northern USSR), and 0.35 deg−1 (south of the Caspian Sea) obtained by Nuttli (1973, 1981). The quality factor, computed for each one of these local phases, shows a clear dependence on frequency, increasing from around 100 at 1 Hz to around 1000 at 16 Hz.

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