The University of Southampton
University of Southampton Institutional Repository

Local earthquake magnitude scale and b-value for the Danakil region of Northern Afar

Local earthquake magnitude scale and b-value for the Danakil region of Northern Afar
Local earthquake magnitude scale and b-value for the Danakil region of Northern Afar
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 (ML), 22 station correction factors (C), and 2 distance?dependent factors (n, K) in the equation ML=log(A)?log(A0)+C. The resultant distance correction term is given by ?log(A0)=1.274336log(r/17)?0.000273(r?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 ML 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.
0037-1106
521-531
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Hammond, James O. S.
d5d7a0da-98a7-4c45-8eed-3155120b450f
Kendall, J-Michael
0a1d10dd-0a0a-4b02-aefd-cde8741307ce
Gallacher, Ryan
689f755f-b4a0-4a3b-9959-93c2fae0ac2c
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Goitom, Berhe
2dcaea8e-cdd3-4b05-a4a0-04481da83881
Illsley-Kemp, Finnigan
c24ef4cb-cbf9-4a58-af8d-da9c7eabd84d
Keir, Derek
5616f81f-bf1b-4678-a167-3160b5647c65
Bull, Jonathan
974037fd-544b-458f-98cc-ce8eca89e3c8
Ayele, Atalay
5b4eeb35-d229-4325-8940-d934dab7563d
Hammond, James O. S.
d5d7a0da-98a7-4c45-8eed-3155120b450f
Kendall, J-Michael
0a1d10dd-0a0a-4b02-aefd-cde8741307ce
Gallacher, Ryan
689f755f-b4a0-4a3b-9959-93c2fae0ac2c
Gernon, Thomas
658041a0-fdd1-4516-85f4-98895a39235e
Goitom, Berhe
2dcaea8e-cdd3-4b05-a4a0-04481da83881

Illsley-Kemp, Finnigan, Keir, Derek, Bull, Jonathan, Ayele, Atalay, Hammond, James O. S., Kendall, J-Michael, Gallacher, Ryan, Gernon, Thomas and Goitom, Berhe (2017) Local earthquake magnitude scale and b-value for the Danakil region of Northern Afar. Bulletin of the Seismological Society of America, 107 (2), 521-531. (doi:10.1785/0120150253).

Record type: Article

Abstract

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 (ML), 22 station correction factors (C), and 2 distance?dependent factors (n, K) in the equation ML=log(A)?log(A0)+C. The resultant distance correction term is given by ?log(A0)=1.274336log(r/17)?0.000273(r?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 ML 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.

Text
DanakilMagnitudeScale5.pdf - Accepted Manuscript
Download (4MB)

More information

Accepted/In Press date: 25 November 2016
e-pub ahead of print date: 24 January 2017
Published date: 1 April 2017
Organisations: Geology & Geophysics

Identifiers

Local EPrints ID: 403528
URI: http://eprints.soton.ac.uk/id/eprint/403528
ISSN: 0037-1106
PURE UUID: 3056a816-02bd-48b3-b2e1-51bb0da78cbe
ORCID for Finnigan Illsley-Kemp: ORCID iD orcid.org/0000-0002-7114-033X
ORCID for Derek Keir: ORCID iD orcid.org/0000-0001-8787-8446
ORCID for Jonathan Bull: ORCID iD orcid.org/0000-0003-3373-5807
ORCID for Thomas Gernon: ORCID iD orcid.org/0000-0002-7717-2092

Catalogue record

Date deposited: 05 Dec 2016 10:32
Last modified: 27 Apr 2022 04:16

Export record

Altmetrics

Contributors

Author: Finnigan Illsley-Kemp ORCID iD
Author: Derek Keir ORCID iD
Author: Jonathan Bull ORCID iD
Author: Atalay Ayele
Author: James O. S. Hammond
Author: J-Michael Kendall
Author: Ryan Gallacher
Author: Thomas Gernon ORCID iD
Author: Berhe Goitom

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×