Abstract
— Factors such as network geometry, network size and phase-picking accuracy have significant effects on the precision of seismic hypocentre locations. In turn, the precision of the hypocentral locations dictates the degree to which morphological details within seismic swarms may be resolved. The Icelandic national seismic network (SIL) is designed to monitor seismic activity across large expanses of Iceland in real-time using automated earthquake detection and location software. Here we examine the performance of the SIL network relative to a much denser, local network of seismometers deployed around the Askja volcano in the Northern Volcanic Zone. A subset of earthquakes from the 2007–2008 dyke intrusion beneath Mt. Upptypp-ingar is used to compare single-and multi-event hypocentral locations. Specifically, we highlight 288, high signal-to-noise ratio events that occurred during an intensive sequence of earthquakes from 6–24 July 2007, when the temporary Askja network was active. A careful refinement of phase onsets recorded by our well-configured, dense network of receivers reveals hypocentres clustered tightly on a planar structure, interpreted as a dyke dipping at 49◦. The root-mean-square (RMS) misfit to the plane (114 m) is only slightly greater than the uncertainties in relative locations of the earthquakes themselves, and constitutes a three-fold reduction in RMS misfit over SIL relative locations. The improved precision, facilitated predominantly by a more favourable network size and configuration, permits a more detailed analysis of the intrusion.
| Original language | English |
|---|---|
| Pages (from-to) | 47-66 |
| Number of pages | 20 |
| Journal | Jokull |
| Volume | 2010 |
| Issue number | 60 |
| State | Published - 2010 |
Funding
We thank G. B. Guðmundsson, B. S. Þorbjarnardóttir, and the Icelandic Meteorological Office (IMO) for providing data from six SIL stations, five of which are funded by Landsvirkjun-Power, for use in our analysis as well as the IMO-derived locations for all 2007 Upp-typpingar events. We also appreciate the help of K. Vogfjörð and R. Slunga in clarifying the IMO single-and multi-event location techniques. Seismometers for the ASN were borrowed from the Natural Environment Research Council SEIS-UK facility (loan 842). We thank M. Coffin, J. Eccles, D. Hawthorn, J.-C. Molina Santana, and A. Nowacki for their assistance with the fieldwork. We also acknowledge the helpful suggestions for improvement of the manuscript provided by I. Þ. Bjarnason and one anonymous reviewer. HRM gratefully acknowledges the financial support of the Marshall Aid Commemoration Commission. Dept. Earth Sciences Cambridge contribution number ESC1981. ÁGRIP Nákvæmni í staðsetningum á upptökum jarðskjálfta er meðal annars háð atriðum eins og fjölda og dreifingu mæla innan jarðskjálftamælanetsins og nákvæmni í aflestri bylgjufasa. Með þéttara neti fæst aukin stað-setningarnákvæmni sem gerir kleift að sjá fínni drætti í gerð jarðskorpunnar. Íslenska jarðskjálftamælanet-ið, SIL-kerfið, er hannað til að fylgjast í rauntíma með jarðskjálftavirkni undir landinu og notar til þess sjálf-virkan úrvinnsluhugbúnað. Í þessari grein eru niður-stöður úr SIL-kerfinu bornar saman við niðurstöður úr þéttara neti jarðskjálftamæla, sem rekið var tímabund-ið af vísindamönnum við Cambridge Háskóla, um-hverfis Öskju og Herðubreið. Við vinnslu á gögnum úr þéttara netinu, sem kallast Askja Seismic Network (ASN), eru einnig notuð gögn frá 6 SIL-stöðvum. Í þessum samanburði eru notaðir 288 jarðskjálftar, sem áttu upptök sín við Upptyppinga á tímabilinu 6.–24. júlí 2007 og voru með skýr bylgjugögn. Skoðaðar eru niðurstöður sem fást með tveimur mismunandi að-ferðum. Annars vegar eru skjálftarnir staðsettir einn og einn í einu og hins vegar er öll jarðskjálftaþyrping-in staðsett samtímis. Síðarnefnda aðferðin gefur mun nákvæmari innbyrðis afstöðu á milli skjálftanna (af-stæðar staðsetningar). We thank G. B. Guðmundsson, B. S. Þorbjarnardóttir, and the Icelandic Meteorological Office (IMO) for providing data from six SIL stations, five of which are funded by Landsvirkjun-Power, for use in our analysis as well as the IMO-derived locations for all 2007 Upp-typpingar events. We also appreciate the help of K. Vogfjörð and R. Slunga in clarifying the IMO single-and multi-event location techniques. Seismometers for the ASN were borrowed from the Natural Environ-ment Research Council SEIS-UK facility (loan 842). We thank M. Coffin, J. Eccles, D. Hawthorn, J.-C. Molina Santana, and A. Nowacki for their assistance with the fieldwork. We also acknowledge the helpful suggestions for improvement of the manuscript provided by I. Þ. Bjarnason and one anonymous re-viewer. HRM gratefully acknowledges the financial support of the Marshall Aid Commemoration Com-mission. Dept. Earth Sciences Cambridge contribu-tion number ESC1981. ÁGRIP.
| Funders | Funder number |
|---|---|
| ESC1981 | |
| Natural Environment Research Council |