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Nepal Hazard Risk Assessment
2.3 RETURN PERIOD CALCULATION
For lower return period analysis we basically run the model of PSHA based on report from Seismic
Hazard of Nepal assessment by Department of Mines and Geology. Several sources identified as seen in
Figure 2.7. Detachment area source characterize higher magnitude (and more rare) earthquake. Thrust
fault sources characterized most of moderate and high earthquake in Nepal (magnitude of 6 – 7.3).
Character of detachment zone are described as ((Pandey et al., 2002)):
- Segmentation of the MHT using seismological and geological symptoms
- Assignment of Magnitude on the basis of arc length or surface area
- M>7.3
- Assignment of Mean return period (expert's opinion)
- Adaptation of Characteristic Fault model for PSHA
For thrust and transverse faults the following operations have been carried out to determine source
characteristics:
- Delineation of linear segments from microseismic observations and structural geological map
- M < 6.3 corresponding to approximately 40 km length of linear segments
- Assignment of seismicity parameters from DMG catalogue
- Adaptation of Poisonian model
Overall report of DMG (department of mines and geology) earthquake hazard assessment will be given
in attachment (pdf file).
Figure 2.7. Earthquake sources in Nepal
The analysis evolved on trial and error basis to match parameter from DMG. Flow chart for creating
PGA map for lower return period is provided in Figure 2.8. The latest map result is presented in Figure
2.9. PSHA analysis also produced several return period value, which trend will be used for the
continuous zone of PGA (PGA map provided from NGI).
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