Two new charts have been added to the General Analysis application related to assessing hazard with the frequency-magnitude relationship. The new charts plot various hazard parameters over time, or, by time of day:
Charts / Time Series / Hazard over Time
Charts / Diurnal / Diurnal Hazard
The following parameters can be plotted in each chart (maximum two at a time):
Mmin – The magnitude of completeness. The magnitude, above which the dataset is complete.
b-value – The slope of the Gutenberg-Richter distribution, describes how the frequency of events scales with magnitude.
N at Mref – The number of events (N) above the reference magnitude (Mref, user defined). Note for reference magnitudes less than Mmin, N will not reflect the actual number of events in the database, since it is based on the Gutenberg Richter distribution, assuming a complete dataset.
Hazard Probability – The probability of an event exceeding the design magnitude (user defined) within one year.
Hazard Magnitude – The magnitude that, to a certain reliability (user defined), won’t be exceeded within one year. Hazard Magnitude is essentially the inverse of Hazard Probability.
Each chart is generated by breaking up the data into bins and fitting the Gutenberg-Richter distribution. The bin width can be set in the control panel. Since there can be a lot of variability in the data and fitting procedures, there are also controls to smooth the results, with a user defined bandwidth.
The figure below is an example of the Diurnal Hazard chart, showing how the b-value varies based on the time-of-day. The b-value drops from around 1.3 to 0.7 during shift change. This represents a large difference in hazard, which is highly sensitive to b-value (illustrated in previous post).
Note that the hazard calculations assume a constant b-value within the analysis volume. This can result in an underestimated hazard (explained in the Hazard Iso’s blog post). For more accurate results, use the hazard assessment application, where the volume is discretised and the probabilities are integrated together from the small scale, to the larger scale.
If you would like to arrange a root upgrade to get these charts, let us know at firstname.lastname@example.org.