Preliminary earthquake detections from seismic stations installed on Bioko Island, Equatorial Guinea

Bioko Island is a part of Equatorial Guinea located in the Atlantic Ocean off the western 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, 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. The majority of depths are crustal, mostly upper to mid crust. The four stations are still recording and will be serviced in November 2018. At that time, data will be collected, and additional stations will be installed to expand the array.

Our preliminary results show there is seismicity associated with Bioko Island as well as Cameroon. We are intrigued by the location of seismic events from Bioko Island. Many of the events are at the southern end of the island and off-shore. Equatorial Guinea's main export is oil and active derricks are located very near to the coasts. It is possible some of the activity is associated with the volcanoes, while others may stem from drilling operations or resultant changes in the local stress regime.