The estimated PGAs from previous studies at a similar probability of exceedance level are within the range of these findings, although the ranges calculated herein are wider. The seismic hazard map for 10% probability of exceedance in 5 years calculated PGAs from 0.02 to 0.10 g and 0.10 to 0.27 g outside of and within the western branch of the East African Rift Valley System, respectively. Results from the probabilistic seismic hazard analyses was expressed through seismic hazard maps for peak ground acceleration at 10% probability of exceedance in 5, 10, 20, 50, 100 and 500 years, corresponding to return periods of 50, 100, 200, 500, 10 years, respectively. As an example, the seismic hazard results at two sites close to each other showed how different seismic hazards can be. A logic tree accounting for the two ground motion prediction equations and dividing the study region into four seismic zones was used for calculating the seismic hazard. This catalog was homogenized to moment magnitude to match with the selected ground motion prediction equations from Toro and Idriss. Using online sources, an earthquake catalog for Uganda and the immediate areas around Uganda was compiled spanning 108 years, from 1912 to 2020. A probabilistic seismic hazard analysis requires the availability of an earthquake catalog, relevant ground motion prediction equations, and an outline of how the hazard calculations will be conducted. A probabilistic approach has been used to assess the seismic hazard for Uganda and the surrounding areas. Seismicity vs.Uganda is situated between the two seismically active branches of the East African Rift Valley System, which are characterized by high levels of seismicity.How do I change my event magnitude marker?.Switch between solid surface and wireframe mode.Why are the event magnitudes different in mXrap?.Where is the cumulative energy line on the Omori chart?.What’s the difference between updating the mXrap software and updating the root folder?.What survey formats can be imported into mXrap?.Changes to mXrap interface – right hand side panels.Seismic Hazard – Sensitivity to b-value.Track Seismic Hazard over Time (per volume).Seismic Source Parameters – Quick Guide.Hazard Assessment App – Excavation View.Short-term Response Analysis Application.Analysing seismicity around large events.In some areas, 100 events may represent a very different hazard to 100 events in another area if the b-value varies.Īnother point of interest in the chart is that for areas with b-values above 2, even very high event numbers represent low hazard. This is important to consider when looking at daily activity rates. So, seismic hazard is very sensitive to the b-value of the area. ![]() In other words an increase of 0.3 in b means you need 10 times more events for an equivalent hazard. Note on the chart, N = 1,000 and b = 0.9 gives the same seismic hazard as N = 10,000 and b = 1.2 (approx). Seismic hazard increases with increasing N and decreasing b-value. For a given time span and volume, if N events have been recorded, what is the probability that one of those events was above M design? In this case M design = M L2. The seismic hazard in the chart below can be considered in the following way. But which has more effect on the hazard result? The chart below shows how seismic hazard varies with b-value for N = 1,000, N = 10,000 and N = 100,000. Probabilistic seismic hazard calculations are dependent on the number of events (N) and the b-value.
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