Intensity Lab
MMI Scale › Level X
X

Extreme

Extreme shaking · Very heavy damage potential

PGA
> 124 %g
PGV
> 219 cm/s
I II III IV V VI VII VIII IX X

Most masonry and frame structures destroyed with foundations. Wooden structures and bridges destroyed. Large landslides. Rails bent greatly.

Effects

People & Response

  • Few or no masonry structures remain standing
  • Bridges destroyed; roads impassable

Objects & Furnishings

  • Railroad rails bent greatly
  • Pipelines put completely out of service
  • Dams, dikes, and embankments seriously damaged

Structures & Environment

  • Most masonry and frame structures destroyed with foundations
  • Wooden structures and bridges destroyed
  • Large landslides; broad fissures in ground
  • Fault slipping visible at surface
Typical PGA (ShakeMap) > 124 %g
Typical PGV (ShakeMap) > 219 cm/s
PGA/PGV ranges are approximate; values overlap between adjacent levels. See Instrumental Intensity for details.

Video Example

MMI X shaking example video thumbnail
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Descriptions are verbatim from the USGS MMI Scale, based on Wood & Neumann (1931) and Richter (1958). Source: USGS Modified Mercalli Intensity Scale .

Instrumental intensity values and PGA/PGV ranges from USGS ShakeMap V4 Technical Documentation (Worden et al.). Intensity Lab reports MMI derived via the Worden et al. (2012) GMICE, interpolated from USGS ShakeMap. PGA/PGV ranges are approximate; actual values overlap between adjacent levels.