Three‐dimensional attenuation variations in southern California

Schlotterbeck, Beth A.; Abers, G. A.

doi:10.1029/2001jb000237

Cited by 28 publications

(25 citation statements)

References 50 publications

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“…Rifted regions with elevated geothermal gradients such as the southwestern United States are in general characterized by high attenuation of seismic waves (e.g., Richter, 1958;Hutton and Boore, 1987;Savage and Anderson, 1995). In southern California, high body-wave attenuation in the lower crust beneath the Salton Trough and San Gabriel Mountains is attributed to a combination of high temperatures and partial melt (Schlotterbeck and Abers, 2001). Our results of relatively large amounts of attenuation in the MER are thus not surprising considering the wealth of independent geophysical and geological data that show evidence for partial melt and magma intrusions in the crust and upper mantle beneath the MER and adjacent Ethiopian plateau (e.g., Bastow et al, 2005;Keir et al, 2005;Kendall et al, 2005;Rooney et al, 2005).…”

Section: Discussionmentioning

confidence: 60%

Local Earthquake Magnitude Scale and Seismicity Rate for the Ethiopian Rift

Keir¹,

Stuart²,

Jackson³

et al. 2006

Bulletin of the Seismological Society of America

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A calibrated local earthquake magnitude scale is essential for quantitative analyses of seismicity. In Ethiopia, effective monitoring of earthquakes and resulting assessment of seismic hazard are especially important as regions with seismic and volcanic activity coincide with regions of economic significance and population growth. We have developed a local magnitude (M L ) scale for the northern Main Ethiopian rift (MER) using earthquake data collected during 2001-2003 on 122 three-component broadband seismic stations. Waveform data from 2139 local earthquakes were corrected for instrument response and convolved with the nominal Wood-Anderson torsion seismograph response appropriate for the original definition of local magnitude. The hypocentral distances considered are 5 to 800 km, with the best represented range from 5 to 150 km. A total of 30,908 maximum zero-to-peak amplitudes (A WA ) were incorporated into a direct linear inversion for individual earthquake local magnitudes (M L ), 244 station factors (C), and 2 linear distance-dependent factors (n, K) in the distance correction term, log (A o ), of the equation for local magnitude: M L ‫ס‬ log(A WA ) ‫מ‬ log(A o ) ‫ם‬ C. The resulting distance correction is given by ‫מ‬log(A o ) ‫ס‬ 1.196997log(r/17) ‫ם‬ 0.001066(r ‫מ‬ 17) ‫ם‬ 2, which implies that ground-motion attenuation is relatively high, consistent with ongoing magma intrusion and the presence of shallow magma reservoirs beneath the MER. Station corrections significantly reduce M L residuals and range between ‫24.0ע‬ M L units. The catalog of earthquakes is complete above M L ϳ2.1 and the annual cumulative seismicity rate follows the relation log N ‫ס‬ 4.5 ‫מ‬ 1.13 M L . Our results are critical for accurate routine quantitative analysis of past, current and, future seismicity in Ethiopia.

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Section: Discussionmentioning

confidence: 60%

Local Earthquake Magnitude Scale and Seismicity Rate for the Ethiopian Rift

Keir¹,

Stuart²,

Jackson³

et al. 2006

Bulletin of the Seismological Society of America

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“…High attenuation in southern California is explained by high geothermal gradients beneath the San Gabriel Mountains (Schlotterbeck and Abers, 2001). In the Main Ethiopian rift, the high rate of attenuation is ascribed to the presence of magmatic intrusions and partial melt within the crust .…”

Section: Discussionmentioning

confidence: 99%

“…Seismic energy will attenuate at varying rates depending on factors such as temperature, composition, and fluid content of the crust as well as partial melt and magmatic intrusions (Schlotterbeck and Abers, 2001;Carletti and Gasperini, 2003;Keir et al, 2006;Wang et al, 2009). This rate of attenuation is characterized by an attenuation curve.…”

Section: Introductionmentioning

confidence: 99%

Local Earthquake Magnitude Scale andb‐Value for the Danakil Region of Northern Afar

Illsley‐Kemp¹,

Keir²,

Bull³

et al. 2017

Bulletin of the Seismological Society of America

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The Danakil region of northern Afar is an area of ongoing seismic and volcanic activity caused by the final stages of continental breakup. To improve the quantification of seismicity, we developed a calibrated local earthquake magnitude scale. The accurate calculation of earthquake magnitudes allows the estimation of b-values and maximum magnitudes, both of which are essential for seismic-hazard analysis. Earthquake data collected between February 2011 and February 2013 on 11 three-component broadband seismometers were analyzed. A total of 4275 earthquakes were recorded over hypocentral distances ranging from 0 to 400 km. A total of 32,904 zero-to-peak amplitude measurements (A) were measured on the seismometer's horizontal components and were incorporated into a direct linear inversion that solved for all individual local earthquake magnitudes (M L ), 22 station correction factors (C), and 2 distance-dependent factors (n, K) in the equation M L logA− logA 0 C. The resultant distance correction term is given by − logA 0 1:274336 logr=17 − 0:000273r − 17 2. This distance correction term suggests that attenuation in the upper and mid-crust of northern Afar is relatively high, consistent with the presence of magmatic intrusions and partial melt. In contrast, attenuation in the lower crust and uppermost mantle is anomalously low, interpreted to be caused by a high melt fraction causing attenuation to occur outside the seismic frequency band. The calculated station corrections serve to reduce the M L residuals significantly but do not show a correlation with regional geology. The cumulative seismicity rate produces a b-value of 0:9 0:06, which is higher than most regions of continental rifting yet lower than values recorded at midocean ridges, further supporting the hypothesis that northern Afar is transitioning to seafloor spreading.Electronic Supplement: List of all local earthquakes used in the study with calculated local magnitudes and associated magnitude error.

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“…Schlotterbeck and Abers (2001) fit theoretical spectra to observed spectra using the leastsquare minimization method of Hough et al (1988), and determined t Ã for P-and S-waves at frequencies between 0.5 and 25 Hz. Schlotterbeck and Abers (2001) fit theoretical spectra to observed spectra using the leastsquare minimization method of Hough et al (1988), and determined t Ã for P-and S-waves at frequencies between 0.5 and 25 Hz.…”

Section: Tomographic Mapping Of Crustal Qmentioning

confidence: 99%