Earthquake catalog from a year+ of seismic monitoring on Bioko Island,
Equatorial Guinea
Abstract
Equatorial Guinea’s Bioko Island is located in the Atlantic Ocean off
the west coast of Cameroon. It is a volcanic island and the first
off-shore expression of the Cameroon Volcanic Line. It is home to three
shield volcanoes: Pico de Basile, Pico Biao, and Gran Caldera de Luba.
Eruptive history is only known for Pico de Basile which erupted within
the past 100 years, and steam vents were observed as recently as 2012.
There is no permanent seismic monitoring; the closest seismic stations
are in Cameroon and have not reported data since 2015. In Nov. 2017
Drexel University researchers, supported by the Bioko Biodiversity
Protection Program (BBPP) and the Universidad Nacional de Guinea
Ecuatorial (UNGE), installed 4 broadband seismometers. Two more stations
were installed in March of 2019. Due to the COVID-19 pandemic data from
the two most recent stations has yet to be retrieved and analyzed. Local
collaborators reported a station was vandalized. It is unknown at this
time how much data was recorded by this station. Preliminary earthquake
detection and location was completed using an automated STA/LTA
algorithm. S wave arrivals were added manually. Initial locations use
the global IASP91 model and events were relocated using a local model.
Events cluster into two areas: those near Bioko Island and those near
Cameroon. Between 12-Dec-2017 and 17-Feb-2018, 77 events were recorded.
Local magnitudes range between 0.16 and 2.61. Of these events, 49 are
located near Cameroon and 28 are near Bioko. Most of the depths are
upper to mid-crust. Analysis of the entire data set yields 458 events
with 367 near Bioko Island and 91 near Cameroon. The range in local
magnitude is -0.28 – 3.86. Our preliminary results show seismicity
associated with Bioko Island as well as Cameroon. Locations match well
with events recorded by a regional network in Cameroon. Stations were
serviced in Feb. and Nov. 2018 and March 2019. Failures have been due to
water infiltration, vandalism, and heavy cloud cover. Enclosures were
redesigned after the Feb. 2018 service. All stations were upgraded to
the new design in Nov. 2018 and solar panels were upgraded (20 to 35
watt) in March 2019. The next anticipated service was to be completed in
March 2020 but was canceled due to the COVID-19 pandemic. The next
anticipated service will occur in March 2022 if travel restrictions
allow.