## Abstract

A local magnitude scale is developed for Tanzania, East Africa, using data collected by the 1994/1995 Tanzania Broadband Seismic Experiment. The waveform data from 1189 local and regional earthquakes located within East Africa were corrected for instrument response and convolved with the nominal Wood-Anderson torsion seismograph response appropriate for the original definition of local magnitude. A total of 24,710 maxium S-wave amplitudes were incorporated into an iterative regression for individual event local magnitudes, 38 horizontal component station factors, and 2 linear distance-dependent factors in the log A_{o} terms of the equation for M_{L}. The resulting distance correction, log A_{o}, is given by -log A_{o} = 0.76 (log(r/17) + 0.000902(r-17) + 2.0, where r is hypocentral distance in kilometers. This distance correction yields much less ground-motion attenuation than observed for southern California and is similar to that observed for local S waves and regional Lg waves propagating in eastern North America. Normalizing the distance correction using the standard constraint of 1-mm ground motion at 100 km for a magnitude 3.0 earthquake results in a bias of nearly half of a magnitude unit between m_{b} and M_{L}, with M_{L} being larger. Normalizing using the constraint of 10 mm of motion at 17 km for M_{L} 3.0 removes the bias in magnitude measures and indicates that structure within Tanzania is relatively high Q. The seismicity distribution and is seen to follow the relation log N=4.63 - 0.84 M_{L}, where N is the number of earthqukes per year of local magnitude M_{L} or greater. The catalog of events used in this study is seen to be complete to magnitude of 2 to 2.5.

Original language | English (US) |
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Pages (from-to) | 712-721 |

Number of pages | 10 |

Journal | Bulletin of the Seismological Society of America |

Volume | 88 |

Issue number | 3 |

State | Published - Jun 1998 |

## All Science Journal Classification (ASJC) codes

- Geophysics
- Geochemistry and Petrology