Long-period regional wave moment tensor inversion for earthquakes in the western United States

1995 ◽  
Vol 100 (B6) ◽  
pp. 9853-9864 ◽  
Author(s):  
Jeroen Ritsema ◽  
Thorne Lay
Keyword(s):  
United States ◽  
Moment Tensor ◽  
Moment Tensor Inversion ◽  
Western United States ◽  
Long Period

Sp phases from the transition zone between the upper and lower mantle

1980 ◽  
Vol 70 (2) ◽  
pp. 487-508
Author(s):  
Sonja Faber ◽  
Gerhard MÜller
Keyword(s):  
United States ◽  
Transition Zone ◽  
Lower Mantle ◽  
The United States ◽  
P Wave ◽  
Western United States ◽  
Nodal Plane ◽  
Transition Zones ◽  
Velocity Models ◽  
Long Period

abstract Precursors to S and SKS were observed in long-period SRO and WWSSN seismograms of the Romanian earthquake of March 4, 1977, recorded in the United States at distances from 68° to 93°. According to the fault-plane solution, the stations were close to a nodal plane and SV radiation was optimum in their direction. Particle-motion diagrams, constructed from the digital data of the SRO station ANMO (distance 89.1°), show the P-wave character of the precursors. Several interpretations are discussed; the most plausible is that the precursors are Sp phases generated by conversion from S to P below the station. The travel-time differences between S or SKS and Sp are about 60 sec and indicate conversion in the transition zone between the upper and lower mantle. Sp conversions were also observed at long-period WWSSN stations in the western United States for 2 Tonga-Fiji deep-focus earthquakes (distances from 82° to 96°). Special emphasis is given in this paper to the calculation of theoretical seismograms, both for Sp precursors and the P-wave coda, including high-order multiples such as sP4 which may arrive simultaneously with Sp. The Sp calculations show: (1) the conversions produced by S, ScS, and SKS at interfaces or transition zones between the upper and lower mantle form a complicated interference pattern, and (2) conversion at transition zones is less effective than at first-order discontinuities only if their thickness is greater than about half a wavelength of S waves. As a consequence, details of the velocity structure between the upper and lower mantle can only be determined within these limits from long-period Sp observations. Our observations are compatible with velocity models having pronounced transition zones at depths of 400 and 670 km as have been proposed for the western United States, and they exclude much smoother structures. Our study suggests that long-period Sp precursors from pure thrust or normal-fault earthquakes, observed at distances from 70° to 95° close to a nodal plane and at azimuths roughly perpendicular to its strike, offer a simple means for qualitative mapping of the sharpness of the transition zones between the upper and lower mantle.

scholarly journals Moment tensor inversion for near earthquakes using long-period digital seismograms.

1989 ◽  
Vol 37 (1) ◽  
pp. 1-29 ◽  
Author(s):  
Takeshi FUKUSHIMA ◽  
Daisuke SUETSUGU ◽  
Ichiro NAKANISHI ◽  
Isao YAMADA
Keyword(s):  
Moment Tensor ◽  
Moment Tensor Inversion ◽  
Long Period ◽  
Digital Seismograms

Age and paleoclimatic significance of late Holocene lakes in the Carson Sink, NV, USA

2003 ◽  
Vol 60 (3) ◽  
pp. 294-306 ◽  
Author(s):  
Kenneth D. Adams
Keyword(s):  
United States ◽  
Tree Ring ◽  
Great Basin ◽  
Late Pleistocene ◽  
Lake Level ◽  
Late Holocene ◽  
Western United States ◽  
Long Period ◽  
Paleoclimatic Significance ◽  
Original Interpretation

AbstractNew dating in the Carson Sink at the termini of the Humboldt and Carson rivers in the Great Basin of the western United States indicates that lakes reached elevations of 1204 and 1198 m between 915 and 652 and between 1519 and 1308 cal yr B.P., respectively. These dates confirm Morrison's original interpretation (Lake Lahontan: Geology of the Southern Carson Desert, Professional Paper 40, U.S. Geol. Survey, 1964) that these shorelines are late Holocene features, rather than late Pleistocene as interpreted by later researchers. Paleohydrologic modeling suggests that discharge into the Carson Sink must have been increased by a factor of about four, and maintained for decades, to account for the 1204-m lake stand. The hydrologic effects of diversions of the Walker River to the Carson Sink were probably not sufficient, by themselves, to account for the late Holocene lake-level rises. The decadal-long period of increased runoff represented by the 1204-m lake is also reflected in other lake records and in tree ring records from the western United States.

Moment tensor inversion of very long period seismic signals from Strombolian eruptions of Erebus Volcano

2008 ◽  
Vol 177 (3) ◽  
pp. 635-647 ◽  
Author(s):  
R. Aster ◽  
D. Zandomeneghi ◽  
S. Mah ◽  
S. McNamara ◽  
D.B. Henderson ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Moment Tensor Inversion ◽  
Seismic Signals ◽  
Long Period ◽  
Strombolian Eruptions ◽  
Erebus Volcano

Aspects of Pn and Pg propagation at regional distances

1982 ◽  
Vol 72 (2) ◽  
pp. 457-471
Author(s):  
Charles A. Langston
Keyword(s):  
United States ◽  
Moment Tensor ◽  
High Amplitude ◽  
Western United States ◽  
Horizontal Distance ◽  
Ray Theory ◽  
Eastern United States ◽  
Crustal Layer ◽  
Head Waves ◽  
Earth Structures

Abstract Generalized ray theory models are calculated for a moment tensor point source in two idealized structure models appropriate for the Eastern United States to study the wave propagation of regional Pn and Pg. The models are analyzed to determine useful discriminants between earthquakes and explosions. Pg is composed of multiply reflected postcritical rays trapped in the upper crustal layer. The amplitude decay with distance of Pg is found to be source dependent and may be useful as a discriminant in well-calibrated earth structures. Pg waves from dip-slip sources fall off r-0.5 to r-0.9 faster than those from isotropic and vertical strike-slip sources, where r is the horizontal distance. In conjunction with previously published refraction results and magnitude studies, it is shown that regional Pn along many profiles in eastern North America consists principally of high-amplitude turning rays rather than head waves as observed in the Western United States. These turning rays are as large or larger than the Pg phase explaining why Pg is not as commonly observed as a distinct phase in the east as compared with observations in the Western United States.

scholarly journals Discrimination of Small Earthquakes and Buried Single-Fired Chemical Explosions at Local Distances (<150  km) in the Western United States from Comparison of Local Magnitude (ML) and Coda Duration Magnitude (MC)

2020 ◽  
Author(s):  
Keith D. Koper ◽  
Monique M. Holt ◽  
Jonathan R. Voyles ◽  
Relu Burlacu ◽  
Moira L. Pyle ◽  
...  
Keyword(s):  
United States ◽  
High Frequency ◽  
Characteristic Curve ◽  
Moment Tensor ◽  
Western United States ◽  
Local Magnitude ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Duration Magnitude ◽  
Chemical Explosions

ABSTRACT Seismologists distinguish underground nuclear explosions from more commonly occurring earthquakes using moment tensor inversion, high-frequency P/S amplitude ratios, mb:Ms comparisons, and P-pP differential travel times. These methods are generally successful for large seismic events (M&gt;3–4) well recorded at regional-to-teleseismic distances (&gt;150  km); however, it is unclear whether they can be modified to work for small events (M&lt;3) well recorded only at local distances (&lt;150  km). Here, we evaluate a recently proposed, local-distance seismic source discriminant—the difference between local magnitude (ML) and coda duration magnitude (MC)—using seismograms of earthquakes and buried, single-fired chemical explosions recorded in three regions of the western United States. The quantity ML–MC was previously found to be sensitive to source depth, effectively discriminating mine blasts, induced earthquakes, and very shallow tectonic earthquakes from deeper crustal earthquakes. In this study, we report the first evaluation of ML–MC as a depth discriminant using data from buried, single-fired explosions that, unlike the seismic sources studied earlier, are good analogs for underground nuclear explosions. We find that even when using generic, uncalibrated methods of assigning magnitudes, ML–MC separates single-fired explosions and earthquakes. The area under the receiver operating characteristic curve is 0.92 for 19 explosions and 14 earthquakes in Washington, 0.90 for 22 explosions and 90 earthquakes in Wyoming, and 0.99 for three explosions and 149 earthquakes in Nevada. ML:MC comparisons have the potential to enhance discrimination based on high-frequency P/S amplitudes ratios—which perform less well at local than regional distances—because the two metrics have complementary sensitivities.

Sign in / Sign up

Export Citation Format

Share Document