Abstract
The main result of this study is the development of attenuation expressions for Modified Mercalli intensity isoseismals in New Zealand earthquakes, in terms of magnitude Mw and source distance. Attenuation of isoseismal intensities has been modelled in a new 2-dimensional manner, i.e. in terms of three distance measures, i.e. radius a along the strike of the fault rupture, radius b normal to strike, and the mean radius c. Other factors which are included in the modelling are depth, focal mechanism, tectonic type (i.e. crustal, interface or dipping slab), and regional variations. As well as being implied in the source distance, the moderate effect of depth (to increase intensities) is modelled well with a separate linear depth term. Shallow (hc ≤ 60 km) Reverse mechanism events were found to give stronger intensities than Strike-Slip events which in tum were stronger than Normal mechanism events, the difference near source between Reverse and Normal events of Mw 7+ events being about 0.4 intensity units. Attenuation for the Central Volcanic Region and Deep events differs markedly from the Main Seismic Region. No magnitude saturation effects were found. Comparisons are made with some earlier New Zealand intensity models, and local and international peak ground acceleration attenuation models.
Highlights
The continued high usefulness of the Modified Mercalli (MM) intensity scale in earthquake hazard and risk assessment has prompted the authors to attempt to improve the modelling of attenuation of intensity in earthquakes in New Zealand
A recent study [35] of attenuation of peak ground acceleration (PGA) in New Zealand earthquakes, found that attenuation of PGA depends on focal mechanism and on depth and on tectonic type (i.e on whether the source was in the interface between the crust and the dipping slab or not)
Attenuation models were developed for subsets of the data by applying multiple regression modelling to the MM intensity data with moment magnitude and functions of source distance being the primary explanatory variables, but with centroid depth, tectonic region, tectonic type, focal mechanism and rake being considered for inclusion in the models
Summary
The main result of this study is the development of attenuation expressions for Modified Mercalli intensity isoseismals in New Zealand earthquakes, in terms of magnitude Mw and source distance. Attenuation of isoseismal intensities has been modelled in a new 2-dimensional manner, i.e. in terms of three distance measures, i.e. radius a along the strike of the fault rupture, radius b normal to strike, and the mean radius c. As well as being implied in the source distance, the moderate effect of depth (to increase intensities) is modelled well with a separate linear depth term. Shallow (he :::; 60 km) Reverse mechanism events were found to give stronger intensities than Strike-Slip events which in tum were stronger than Normal mechanism events, the difference near source between Reverse and Normal events of Mw 7+ events being about 0.4 intensity units. Comparisons are made with some earlier New Zealand intensity models, and local and international peak ground acceleration attenuation models
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Bulletin of the New Zealand Society for Earthquake Engineering
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
