Earth elementals in Oceana are massive, rumbling things, and when they move through earth, they generate earthquake-like shaking and shuddering. Even the largest earth elementals given in the ACKS core book never produce higher than an MI-6 (HD [12] produce MI-5, HD [8] produce MI-4), but since there are elementals of much greater power in Oceana, I wanted to clarify the various MI effects in ACKS-ish terms.
The base area of effect is a 10-foot radius; 30 feet out is one step lower; 100 feet, two steps lower; 300 feet, three steps lower; and so on. For example, an MI-12 earthquake generates MI-5 effects six miles away!
MI-1. Barely detectable in a still, quiet room. Dogs may bark. Up to HD [1–1].
MI-2. Perceptible, and may result in suspended objects swinging. Up to HD [2].
MI-3. Floor vibrates. Suspended objects swing noticeably. Up to HD [4].
MI-4. Walls make creaking or cracking sounds, and the floor noticeably vibrates. Balanced objects fall over. Up to HD [8].
MI-5. Glass windows break. Bells ring. Floor and ground audibly vibrate with low rumble. Up to HD [14].
MI-6. Glass and ceramics break. Shelves topple. Heavy furniture shifts and slides. Walls may show some cosmetic damage. Up to HD [20].
MI-7. Save vs. Paralysis at +4 to stand upright. Furniture and similar unsecured structures take damage, walls will crack (quality construction can ignore this), ground vibration is visible. Up to HD [26].
MI-8. Save vs. Paralysis to stand upright. Most roofs suffer partial collapse, and poorly constructed buildings fall apart. Chimneys, columns, monuments, and other mostly vertical structures are knocked over. Even the heaviest furniture shifts and moves. A collapsing structure will generally deal 2d6 damage per story, with a save vs. Blast halving the damage; a collapsing roof deals 1d6 damage. Up to HD [32].
MI-9. Save vs. Paralysis at –4 to stand upright. Even quality buildings suffer partial collapse, and may shift off the foundation. All objects and creatures on the surface suffer 1d6 damage from the slamming; a save vs. Blast halves this. Collapsing structures deal damage as for MI-8, above. Up to HD [38].
MI-10. Save vs. Paralysis at –6 to stand upright. Most buildings collapse entirely; wooden structures are utterly splintered. Foundations are cracked and damaged. Roads are cracked and sundered. Landslides occur anywhere there is a slope. Collapsing structures deal 3d6 damage per story (save vs. Blast for half) and roofs deal 2d6 in the same fashion. Caverns collapse for 10d6 damage (save vs. Blast for half). Landslides deal 6d6 damage (save vs. Blast for half) and bury everything in their path. All objects and creatures on the surface suffer 2d6 damage from the slamming; a save vs. Blast halves this. Up to HD [44].
MI-11. Save vs. Paralysis at –8 to stand upright. Bridges and buildings are destroyed (damage as above). Landslides, cracks, and deformation of the ground occur. All objects and creatures on the surface suffer 3d6 damage from the slamming; a save vs. Blast halves this. Up to HD [50].
MI-12. Standing upright is impossible. The ground ripples visibly, resembling rocky waters more than solid ground. Hills may shift position. Everything is destroyed. Caverns are completely collapsed. River routes may shift. All objects and creatures on the surface suffer 5d6 damage from the slamming; a save vs. Blast halves this. All larger HD elementals.