Developing and Implementing an International Macroseismic Scale (IMS) for Earthquake Engineering, Earthquake Science, and Rapid Damage Assessment

The USGS “Did You Feel It” (DYFI) is an extremely popular way for members of the public to contribute to earthquake science and earthquake response. DYFI has been in operation for nearly two decades (1999-2019) in the U.S., and for nearly 15 years globally. During that period the amount of data collected is astounding: Over 5 million individual DYFI intensity reports—spanning all magnitude and distance ranges—have been amassed and archived. Several of these types of surveys have been developed by international seismological institutions as well and many of these institutions have implemented algorithms to interpret intensity evaluations automatically, as a rapid and easy way to obtain a geographical distribution of the damage.  

However, these automatic intensity evaluations have a known limitation: they are best for assigning intensity values up to VII in the case of the US and New Zealand MMI. At MMI VII and above, buildings can suffer considerable damage, and the assignment of intensity values requires engineers’ involvement to assess the building’s type and damage level. In the US, the USGS considers that intensities VIII and higher should be evaluated by professionals, so for destructive earthquakes, alternative macroseismic observations (e.g., from engineering reports, press reports and field reconnaissance) should be used. With the need to have seismologists and engineers review the higher intensity assignments, an unsolved problem is how to automatically evaluate and assign higher shaking intensities. We note that USGS no longer maintains staff with macroseismic expertise dedicated to assigning intensities for future earthquakes.  

Moreover, MMI itself is a somewhat outmoded scale compared with the more recently developed system used in much of Europe (EMS-98), which allows for statistics of building damage and distributions. However, in the U.S. (and New Zealand, among other countries) our buildings are not represented in EMS-98, which was developed for Europe, so a globally applicable scale has not taken hold. The main aims of this project, then, are to (1) revise the MMI scale in US/NZ to be compatible with EMS-98, (2) improve US/NZ strategies for rapid macroseismic assignments, particularly for higher intensities, and (3) align these revisions into an update of EMS-98 which will serve the globe as an International Macroseismic Scale (IMS).  

There are three necessary solutions to these challenges. First, we must improve US/NZ strategies for rapid macroseismic assignments, particularly for higher intensities. The EMS-98 scale provides detailed guidelines on how to assign intensities above VIII, by providing (1) a range of vulnerability classes for different building types; (2) a description of the number of buildings in a certain area with each pair vulnerability class/damage grade (e.g., “many buildings of vulnerability class A suffer moderate damage”); (3) a quantitative range for the terms “few”, “many”, “most”; and (4) damage descriptors (on a scale from 0=no damage, to 5=collapse) for masonry and reinforced concrete buildings.  However, the EMS-98 scale is not applicable in US/NZ, as it does not include many of our most common building types. What are missing are the building vulnerability classes and damage grade descriptors suitable for US/NZ structures analogous to those in Europe. Second, as part of this effort, we aim to also greatly facilitate better approaches to assigning macroseismic intensity in the US/NZ by tapping into existing post-earthquake building inspection protocols for inspecting buildings by engineers to assign intensities effectively as a byproduct of their inspections. Lastly, and the focus of our second major workshop, align these strategies back into an update of EMS-98, applicable to the globe, which will become an International Macroseismic Scale (IMS). In the past decade, considerable efforts have been made to create an international macroseismic scale (IMS), based on EMS-98. However, the changes suggested in these documents have not yet been incorporated into a consensus IMS. We aim to do so. 

This proposal is an interesting twist on the Powell Center’s goal of promoting cutting-edge analysis of Earth system information. Here we aim to merge the classical approach to ascribing earthquake shaking and damage employed for centuries, with state-of-the-art data acquisition and internet-based citizen science, in order to facilitate earthquake response, earthquake engineering loss assessments, and for the greater benefit of the world’s population exposed to earthquake risk. Attaining and facilitating the use of a globally applicable IMS would be quite an achievement!