Earthquake swarm associated with volcanic eruption, CuraCoa Reef Area, Northern Tonga, July 1973

S. J. GIBOWICZ, J. H. LATTER, G. K. SUTTON

Abstract


A submarine volcanic eruption near Curagoa Reef, first
observed on 12 J u l y 1973 (U.T.) f r om Tafalii Island, northern Tonga, was
associated with an e a r t h q u a k e swarm in t h e same area. The swarm began
about 03'1 on I I J u l y and died away gradually about 07'' on 13 J u l y , ft
comprised 504 events of magnitude Mi, „2= 3.4, the largest being of magnitude
Ml = 5.1. The swarm area for these comparatively low magnitude earthquakes
was abnormally large
The v a r i a t i o n in r a t e of e a r t h q u a k e occurrence during t h e s w a rm shows
two distinct stages, one similar to t h a t in a foresliock sequence, and t h e other
like t h a t in a n a f t e r s h o c k sequence, with t h e largest events occurring between
t h e two. The average value of b, defining t h e f r e q u e n c y - m a g n i t u d e relationship,
was high: 1.77 ± 0.15. Furthermore, this p a r a m e t e r varied during the
course of t h e swarm, a decrease in t h e b value f r om 1.8 to 1.1 being followed
by a sharp increase to 2.5 a f t e r t h e largest earthquakes and principal volcanic
eruption.
Values of seismic moment were obtained from A B for 118 e a r t h q u a k es
which were well recorded by long-period seismographs. Other source charact
e r i s t i c s were determined from the difference between t h e l o g a r i t hm of seismic
moment and the local magnitude. The source sizes were found to he
u n u s u a l l y large. There was a t i m e variation of source properties during the
swarm. The v a r i a t i o n of t h e displacement shows an inverse correlation with
t h e variation of the coefficient b.
The swarm produced very d i s t i n c t i v e T phases, well recorded at a hydrophone
near Wake Island and at seismograph stations s i t u a t e d on t h e oceanic
side of the Tonga Trench: these were not recorded at seismograph stations
within the island arcs.

Full Text:

PDF

References


DOI: https://doi.org/10.4401/ag-4933
We use cookies to ensure that we give you the best experience on our website. If you continue to use this site we will assume that you are happy with it (Read more).
Ok


Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X