Observation of a New Long‐Period (16‐s) Persistent Tremor Originating in the Gulf of Guinea

A new persistent microseismic tremor, with a narrowband period centered near 16 s, was discovered in the primary microseism spectral peak by analyzing seismic waveforms recorded by African, European, and American seismometers. This tremor may generate coherent arrivals in noise cross‐correlation functions (NCFs), which could potentially bias ambient noise tomography. Using an envelope‐stacking method, we discovered that the 16‐s tremor source is in the coastal region of the Gulf of Guinea and is probably isolated from the previously reported 26‐s tremor source. The nature of the newly identified 16‐s tremor, like the 26‐ and 27‐s tremors, is similar to a volcanic tremor radiated by the Mayotte volcanic system, thereby suggesting that the excitation of all the Gulf of Guinea tremors may be related to volcanic activities. Thus, this study implies that there may still be active volcanoes in the gulf. Plain Language Summary A new persistent and localized microseismic tremor is discovered by quiet African, European, and American seismometers. This tremor has a narrowband period near 16 s, close to the primary microseism spectral peak that is generated by ocean waves in the Earth's shallow coastal regions. The seasonal variation of its amplitude suggests an ocean wave‐related excitation. Examining cross‐correlating seismic records, we observe that the tremor can generate coherent arrivals in interstation surface wave Green's function. Thus, it could impact surface wave dispersion measurements and bias ambient noise tomography. Using envelope stacking of tremor arrivals, the source was found to be constrained to the coastal region of the Gulf of Guinea and possibly isolated from the previously reported 26‐s persistent microseismic tremor source. The nature of the tremor, like the 26‐ and 27‐s tremors, is similar to a recently reported volcanic tremor radiated by the Mayotte volcanic system, suggesting that all of these tremors may be relate to volcanic activities. This study suggests that there still are active volcanoes in the Gulf of Guinea. Key Points A new persistent tremor with a narrowband period centered near 16 s was observed in the primary microseism spectral peak The source of this tremor is located at the shallow coastal region of the Gulf of Guinea and probably isolated from the 26‐s tremor source The Gulf of Guinea tremors may originate in volcanic activities due to the spectral similarity to a tremor in the Mayotte volcanic system