Preliminary earthquake detections from seismic stations installed on
Bioko Island, Equatorial Guinea
Abstract
Equatorial Guinea’s Bioko Island is located in the Atlantic Ocean off
the west coast of Cameroon. Bioko 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 San Carlos. Eruptive
histories are not known for Pico Biao or San Carlos. Pico de Basile
erupted within the past 100 years, and steam vents were observed as
recently as 2012. Malabo, the capital city of Equatorial Guinea, sits in
the shadow of Pico de Basile. There is no permanent seismic monitoring;
the closest seismic stations are in Cameroon and have not reported data
since 2015. In November 2017 Drexel University researchers, supported by
the Bioko Biodiversity Protection Program (BBPP) and the Universidad
Nacional de Guinea Ecuatorial (UNGE), installed 4 broadband
seismometers. In February 2018, the data were retrieved, and stations
serviced. Preliminary earthquake detection and location was completed
using an automated STA/LTA algorithm. S wave arrivals were added
manually. The initial locations use the global IASP91 model and events
were relocated using a local model. The events detected 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 crustal, mostly
upper to mid crust. Our preliminary results show there is seismicity
associated with Bioko Island as well as Cameroon. The locations match
well with events recorded by a local network installed in Cameroon in
2007. The four stations were serviced again in November 2018. One
station failed due to water infiltration and one was vandalized within a
week of the previous service. One station was still operational at
service with only a few days down and the last station was operational
until the height of the rainy season when power failed.