A review of the seismicity of the Cameroon Volcanic Line observed by two local seismic networks

Abstract:

The Cameroon Volcanic Line (CVL) is a linear feature of volcanism that begins off the western coast of Africa with several islands and continues on shore through Cameroon further into the African continent. Equatorial Guinea’s Bioko Island is the largest and last of the CVL volcanic islands. 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. The CVL is of scientific interest and has been studied by several groups. Most geophysical studies focus on the area around Mt. Cameroon, the most active volcano in the system. A network of seismic stations was installed across the entire country from 2005-2007. There has been no successful geophysical surveys of the island portion of the line.

In Nov-2017 Drexel University, supported by the Bioko Biodiversity Protection Program (BBPP) and the Universidad Nacional de Guinea Ecuatorial (UNGE), installed 4 broadband seismometers on Bioko. Two stations were installed in March of 2019. Preliminary earthquake detection and location was completed with an automated STA/LTA algorithm. Initial locations use the global IASP91 model and events were relocated with a local model. Events cluster in 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 the regional network previously installed in Cameroon. In addition, the rate of seismicity recorded from 2017-2019 is comparable to what was observed from the Cameroon network when distance is taken into account. Data has been retrieved in Feb-2018, Nov-2018, and Mar-2019. The next service was scheduled Mar-2020 but the trip was canceled due to travel restrictions.