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Solving the Mystery of Orphan Tremors Detected in Western Africa on Sept 5-7, 2018
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  • Tolulope Morayo Olugboji,
  • Yingping Lu,
  • Adekunle Abraham Adepelumi,
  • Folarin Kolawole,
  • Manoochehr Shirzaei
Tolulope Morayo Olugboji
University of Rochester, University of Rochester, University of Rochester

Corresponding Author:tolumorayo@gmail.com

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Yingping Lu
University of Rochester, University of Rochester, University of Rochester
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Adekunle Abraham Adepelumi
OAU, Ife, Nigeria, OAU, Ife, Nigeria, OAU, Ife, Nigeria
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Folarin Kolawole
University of Oklahoma, University of Oklahoma, University of Oklahoma
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Manoochehr Shirzaei
Virginia Tech, Virginia Tech
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On September 5-7, 2018, a series of puzzling tremors were reported in the capital city of Nigeria in Mpape, Abuja. This event follows a growing list of tremors experienced in a stable intra-plate region not expected to be earthquake-prone. Initial speculation suggested that the shaking resulted from anthropogenic activity related to ground-water extraction, although no corroborating geophysical, or seismic evidence exists to confirm such a hypothesis. Here, we identify the parent location of this orphan tremor by developing a technique for the single-station location of seismic sources, an approach particularly suited for regions with sparse seismic networks. Our procedure identifies the spatial origin of incoming seismic waves by using a combination of energy and polarization filters to robustly identify seismic phases and extract differential time (epicentral distance) and arrival azimuth. We demonstrate that our technique can discriminate between local, regional or teleseismic events. We apply this technique to the 3-day seismic record obtained from select stations around Nigeria. We rule out western-Africa as the origin of the reported tremors. A comprehensive scan of the available seismic record suggests that the source of the felt tremors was coincident with the earthquake which was reported to have triggered massive landslides. We hypothesize that these landslides generated enough low-frequency single-force surface-collapse, strong enough to be preferentially amplified by the local geologic structure of the Abuja area.