Earthquake Weather

by Stephen Dedman

Like Dracula, Frankenstein's monster, and many other cinematic horrors, the disaster movie steadfastly refuses to die. Earthquakes, volcanoes, floods, fires, avalanches, meteor strikes, shipwrecks, plane crashes, giant creatures or hordes of smaller ones -- they all come back, hoping to thrill us with special effects and schadenfreude.

GURPS already caters for GMs who want to use some of the standard disaster movie plots. GURPS Basic and Compendium II deal with fire, extremes of temperature, radiation, and vehicle collisions. Giant creatures and hordes are covered in GURPS Bestiary or GURPS Atomic Horror. Atomic Horror also has rules for volcanoes, and GURPS Cliffhangers has rules for sandstorms. GURPS Y2K boasts chapters on the Apocalypse, survivors, and a list of disaster movie clichés. But if you want an earthquake, a tsunami, a tornado, or a meteor strike . . . you've come to the right place.

The following rules may be useful for high-powered spellcasters or supervillains wanting to destroy a town or fortress -- or for the GM dispatching heroes (super-powered or otherwise) to try to save as many lives as possible from a cataclysm, either in an evacuation or a rescue mission. They can also be useful for the GURPS Time Travel GM who wants to send heroes back to take what they can from a city before it's leveled, or the GURPS Space GM wanting to create a planet where natural disasters are common but the wealth tempts many to brave the dangers.


Earthquakes are usually brief, lasting only 2d × 5 turns (the 1906 San Francisco quake lasted 45-60 seconds). Quakes are often followed by aftershocks, usually of lesser intensity.

The best known measure for earthquake intensity is the Richter Scale, but the Mercalli Scale, which measures earthquake damage, may be more useful for GMs. Quakes below VII on the Mercalli Scale or 5 on the Richter Scale (Tiny spell result) are usually negligible in gaming terms.

Mercalli VII/Richter 5/Mild Earthquake spell: Felt by all. Items fall from shelves, furniture may overturn or break, bells ring. Adobe, masonry and concrete may crack, loose bricks and tiles fall. Fright Check needed, at -1 for characters on second story, -2 for higher floors. Roll vs DX or ST every turn to walk without falling, taking 1d damage.

Falling object damage: characters or vehicles indoors, or in built-up areas, hit by debris on a Very Bad reaction roll; roll 1d and consult Table A.

Mercalli VIII/Richter 6/Severe Earthquake spell: Stone walls damaged; walls, chimneys, and towers may fall. Cracks in wet ground and steep slopes. Branches fall from trees. Fright Checks at -2. Roll vs DX-3 or ST-3 every turn to walk without falling, taking 1d damage. Roll vs Driving to keep control of moving ground vehicles.

Falling object damage: characters or vehicles indoors, or in built-up or forested areas, hit by debris on a Bad or worse reaction roll; roll 1d+2, and consult Table A.

Mercalli IX/Richter 7 to 7.4/1989 San Francisco Quake: Poorly constructed buildings destroyed, ordinary buildings and dams badly damaged. Underground pipes break, causing gas leaks and potential fires. Conspicuous cracks in ground; sand flows like liquid. Fright Checks at -4. Roll vs DX-4 or ST-4 to walk without falling (taking 1d damage). Roll vs Driving at -2 to keep control of moving ground vehicles. Characters may be trapped in confined spaces by structural damage fallen roofs, collapsed stairways, blocked doors, etc.

Falling object damage: Characters or vehicles indoors, or in built-up or forested areas, hit by debris on a Bad or worse reaction roll. Roll 2d and consult Table A.

Mercalli X/Richter 7.5 to 7.9: Most buildings and bridges destroyed, unless steel-framed; large dams badly damaged, possibly causing flash floods. Rails bend slightly. Major landslides. Fright Checks at -5. Roll vs DX-5 or ST-5 to walk without falling. Roll vs Driving-4 to keep control of moving ground vehicles.

Falling object damage: Characters or vehicles indoors, or in built-up or forested areas, hit by debris on a Bad or worse reaction roll. Roll 2d+2 and consult Table A.

Mercalli XI/Richter 8 to 8.4/1906 San Franciso Quake: Steel-framed buildings destroyed; rails bend severely, and underground pipelines fail. Roll vs Driving-5 to keep control of moving ground vehicles. 1% of population killed by quake or aftermath; 50% homeless. Otherwise, as Mercalli X.

Falling object damage: Characters or vehicles indoors, or in built-up or forested areas, hit by debris on a Poor or worse reaction roll. Roll 3d and consult Table A.

Mercalli XII/Richter 8.5+/The "Great Quake" of GURPS Deadlands, or the opening of the Sixth Seal (p.Y2K117). Damage nearly total. Large rock masses displaced. Lines of sight and level distorted. Objects thrown into the air. Attempts to move on any surface in a straight line -- driving, climbing, landing aircraft, etc. -- only possible on a critical success.

Falling object damage: characters or vehicles indoors, or in built-up or forested areas, hit by debris on a Poor or worse reaction roll. Roll 2d+6 and consult Table A.

Avalanches and Landslides

Landslides can be caused by earthquakes, volcanoes, or as a result of erosion caused by a fire or flood. For GURPS purposes, an avalanche or landslide is a huge mass of falling objects -- but one that might possibly be survived.

Using the rules on p.B131, treat the bulk of the debris as being tipped over onto the heroes (or their vehicle), rather than falling freely, and divide the effective weight (and therefore the damage) by 100. Further, snow and mud (but not rock) can be treated as soft, halving the damage. Therefore, it would be possible for a normal PC to be hit by ten tons of debris and (assuming he also lands on something soft, such as snow or mud), take only 10d damage. However, he would then be at least partially buried under the debris, and may be in danger of suffocating (see p. B91). Even if he can breathe, he may still be killed by cold (p. B130) or thirst (p. B128), or bleed to death (p. B130), if he isn't rescued and can't dig himself out.

A slightly more merciful variant on this would be to have characters mostly unhurt but trapped inside a buried or sunken vehicle or other form of shelter, a la Airport '77 or Arthur C. Clarke's novel A Fall of Moondust.

Flows of volcanic ash and mud have been clocked at 80 mph, and a 3000' wide avalanche triggered by a 7.7 magnitude quake in Peru in 1970 reached an estimated 248 mph, but this is exceptional. Most landslides move at 10 to 35 (5d+5) mph, so outrunning one to reach safe ground might be possible. If the PCs have Skiing skill but have never used it, this may be their chance.


Strong winds -- hurricanes and tornadoes -- can be as destructive as earthquakes, and last much longer. Fortunately, they're much easier to predict and prepare for; a successful Meteorology roll can predict a storm 6 hours in advance at TL 6-, and much longer after the invention of weather satellites at early TL7. (Whether predicting earthquakes and volcanic eruptions becomes routine at higher TLs is up to the GM.)

Thunderstorms can advance at 70 mph in strings hundreds of miles across, bringing gale-force winds, heavy rain or hail, as well as lightning.

Naturally-forming tornadoes are 100-300 yards wide and travel at 30-60 mph. Duration is usually less than twenty minutes, but the record (the Great Tri-State Tornado) was a mile in diameter at its peak, lasted three and a half hours, and wreaked damage on a path 219 miles long, killing 695 people and permanently destroying some towns. Tornadoes also bring heavy rain, and often hail.

Hurricanes range from five to 400 miles in diameter. Naturally-forming hurricanes may last for weeks at sea, but dissipate within 24 hours of coming inland (another good way to trap characters in a confined space). They may still reach hundreds of miles inland, and produce tornadoes that wreak further damage.

Much hurricane damage is caused by "storm surge," flooding from a rising sea level as they hit the shore -- from 5' to a recorded 48' higher than normal tides, along a front of 50-100 miles. They also bring 10-20" of heavy rain, which may exacerbate flood damage. See Flood, below.

For gaming purposes, the most useful measure of wind strength is speed in mph, but other scales that may crop up in weather reports include the Beaufort Wind Force Scale (Calm to Hurricane), the Saffir-Simpson hurricane intensity scale (Minimal to Catastrophic), and the Fujita-Pearson Scale for tornado damage (Gale to Inconceivable).

Rules for the effects of non-destructive wind (less than 50 mph) are given on p. B188.

50-74 mph: Gale; Windstorm spell. Characters in the open must roll vs. ST each turn to avoid being knocked over. All DX-based skills (including vehicle skills) are at -5 (-10 for wind-powered vehicles); ranged attacks succeed only on a critical hit. Small trees uprooted, minor damage to buildings (loose tiles dislodged, etc.) and mobile homes, boats torn from moorings.

75-110 mph: Hurricane; Cyclone; Typhoon; Moderate Tornado; Whirlwind spell/super-power. As above, except that ST rolls are at -5, visibility is reduced to one hex. Picks up objects of up to 30 lbs per hex radius, for spell or power; for natural causes, picks up objects of up to 1d×30 lbs. Large trees blown down; roofs, doors and windows damaged. Mobile homes destroyed.

Flying debris damage: roll every turn. Characters or vehicles in the open hit by debris on a Very Bad reaction roll; roll 1d and consult Table A.

111-149 mph: Intense/Major Hurricane; Significant Tornado. As above, but damage extensive, all signs down, most small buildings roofless. Witnesses make Fright Checks. All vehicle skills at -10.

Flying debris damage: roll every turn. Characters or vehicles in the open hit by debris on a Bad or Worse reaction roll; roll 2d and consult Table A.

150-206 mph: Super-typhoon; Severe Tornado; Category 4 to 5 (Extreme to Catastrophic) Storm. Window glass shatters, small buildings blown away, major damage to larger buildings, many vehicles (including light aircraft) overturned, most trees uprooted. Vehicle use impossible; Fright Checks at -2. 10% of population homeless.

Flying debris damage: roll every turn. Characters or vehicles in the open hit by debris on a Bad or Worse reaction roll; roll 2d+3 and consult Table A.

207-260 mph: Devastating Tornado. As above, but most houses leveled or blown away, and cars and other large missiles thrown about. Fright Checks at -4.

Flying debris damage: roll every turn. Characters or vehicles in the open hit by debris on a Bad or Worse reaction roll; roll 3d and consult Table A.

261-318 mph: Incredible Tornado. As above, but reinforced buildings badly damaged; cars blown more than 100 yards.

Flying debris damage: roll every turn. Characters or vehicles in the open hit by debris on a Poor or Worse reaction roll; roll 3d and consult Table A.

318-379 mph: Inconceivable Tornado. Very unlikely, except over small areas. As above.

Flying debris damage: roll every turn. Characters or vehicles in the open hit by debris on a Poor or Worse reaction roll; roll 2d+6 and consult Table A.


For a wildfire or burning skyscraper scenario, use the rules on pp. B129-130; place hexes of fire where you will, and move them at whatever speed you feel is justified (many forest fires are fanned by strong winds, and may much move faster than humans can run, especially over bad terrain). Remember that smoke (p. B132) will knock many people out, preventing them escaping the flames.

A burning building (or forest) may also begin to collapse if damaged by fire, showering anyone trapped there with debris; roll on Table A as appropriate. This debris may also be burning, adding 1d-1 damage.

Animals (including venomous snakes) will also try to escape forest fires, and may attack humans who are in their path.


Though lightning kills over 200 people in an average year in the USA (not including deaths caused by the fires that lightning starts), it's a sufficiently unusual cause of death that many religions have regarded it as a weapon of some god. After Franklin invented the lightning rod, churches were briefly forbidden to use them because it was seen as circumventing God's will. PCs should probably not be hit by naturally occurring lightning unless they have the Cursed disadvantage, or are brandishing a metal object during a thunderstorm (a golf club, radio aerial, sword, etc.). Treat a lightning bolt as a lethal electrical shock (p. CII138), doing 3d to 12d damage.


Floods are the second-most common of natural disasters (after fires). Flash floods kill an average of 200 people, and cause more than $1 billion damage, each year in the USA. Flash floods may be caused by rivers overflowing from heavy rain or snow-melt, or by tsunamis, dam-bursts, or storm surge from hurricanes, etc.

Even slow-rising waters can carry vehicles away, destroy roads and bridges, and cause major property damage; however, all it may take to survive such a flood is a roll vs. IQ or Area Knowledge +4 (to find higher ground) and possibly Climbing (to reach it). Most people killed by floods were trying to save their families, pets, or property (often cars, which cope less well with floods than people). This may be bad news for characters with disadvantages such as Dependents, Sense of Duty, Miserliness, Greed, etc.

Characters unexpectedly caught by a flash flood must roll ST to remain standing. If they were knocked down, or if the water is over their heads (e.g. more than 6' deep, for most PCs), they must then roll vs. Swimming at -5 to avoid drowning (usual modifiers apply: see p. B91). If not, they have a choice of swimming or wading to higher ground. If the water is freezing (e.g. recent snow melt), use the rules on p. CII135.

Characters caught in flood waters may also be hit by debris on a Bad or worse result: roll once per turn. Roll 1d if the water is less than 1 yard deep, 2d if 1-2 yards deep, 3d if more than 2 yards deep, and consult Table A.


A tsunami is a wave or series of waves generated by an undersea disturbance (earthquake, landslide, volcanic eruption, or meteor strike). Tsunamis may grow to over 100' high as they near a coastline, hurling boats and debris up to a mile inland. The waves move across the sea at an average 450 mph, and usually strike 10 to 45 minutes apart.

After the Krakatoa explosion, 130' waves hit Java and Sumatra, hurling a warship half a mile inland. More typical waves are 10'-40' high (6d+4'), and Slam (p. B112) with an ST equal to their height, potentially doing knockback (p. B106), with 2d crushing damage if the victim is pushed into a wall or other hard object (otherwise, 1d). Characters caught by the wave should then treat it as a flash flood (above) of the appropriate depth.

Ships have successfully negotiated tsunamis and escaped undamaged; this requires a critical success on the appropriate vehicle skill (Boating, Powerboat, Seamanship, or even Surfing).


A typical naturally occurring hailstorm lasts less than an hour (10d minutes), and covers an area a half mile wide by five long. Hailstones as large as grapefruit, weighing nearly two pounds, have been documented; these can cause major damage to crops, buildings, vehicles, livestock, and occasionally to people unlucky or foolhardy enough to be caught out in the open. These severe hailstorms do 1d-2 crushing damage per turn, the same as a damaging Hail Spell (p. M37). Less severe hail merely provides distractions and slows down travel in the same way as rain (p. B187).


A blizzard is marked by winds over 35 mph, visibility of no more than 660' (unless the character has an Ice Vision spell or similar super-power), and a temperature below freezing. A severe blizzard has winds over 47 mph (treat as a gale, above), temperature below 10 Fahrenheit (roll vs. HT or Arctic Survival every 30 minutes; see p. B130), and near-zero visibility (treat as a Whiteout; see p. CII134).

Meteor Strike

Houses, cars and people have been hit by meteors, and one dog has been killed by a direct impact, but a big meteor can wreak havoc even if it strikes miles away from the PCs. Major meteor or comet strikes cause earsplitting airblasts, thermal radiation, and earthquakes. They also bombard a huge area with debris if they hit land, or cause tsunamis if they hit water.

Meteoroids less than two feet in diameter entering an Earth-standard atmosphere vaporize before reaching the surface, doing no damage (thinner atmospheres offer less protection, but even trace atmospheres offer a little). A shower of 2' meteoroids could carpet-bomb an area, each one doing 6d×4 concussion damage and 1d-2 fragmentation damage (see pp. CII64-65) and leaving craters up to 277' in diameter, but for destruction on disaster movie scale, you need bigger rocks.

An M-type (metal) meteor 6'3" in diameter, hitting soil, porous rock or a built-up area, is equivalent to a 1 kiloton explosion and leaves a crater 673' in diameter. Concussion damage is 12d×2,000,000; quarter concussion damage for every 128 yards from the impact site (see p. CII64).

An M-type (metal) meteor 13'6" in diameter or S-type (stony/iron) meteor 19' in diameter, hitting soil, porous rock or a built-up area, is equivalent to a 10 kiloton explosion (similar to the bomb dropped on Hiroshima, but without radioactive fallout) and leaves a crater 1155' in diameter. Concussion damage is 12d×20,000,000; quarter concussion damage for every 256 yards from the impact site.

A meteor 40' in diameter hits with an impact equivalent to 100 kilotons of TNT, and leaves a crater 2063' in diameter. Concussion damage is 12d×200,000,000; quarter concussion damage for every 512 yards from the impact site.

A meteor 87' in diameter hits with an impact equivalent to a 1 Megaton bomb, and leaves a crater 3783' in diameter. Concussion damage is 12d×2,000,000,000; quarter concussion damage for every 1,024 yards from the impact site.

A meteor 402' in diameter strikes like a 100 Megaton bomb, leaves a crater 1.71 miles across, and shatters windows 50 miles away with its airblast. Concussion damage is 12d×200,000,000,000; quarter concussion damage for every 4,096 yards from the impact site.

A modest comet, two miles across, leaves a crater 34.82 miles in diameter, and is felt as a Mercalli VII earthquake up to 380 miles away. If it hits water instead, this will manifest as tsunamis -- but in either case, the airblast will do the same damage as a Super-Typhoon. The fireball will be visible from 170 miles away, and thermal radiation will cause 3d burn damage to people up to 250 miles away and may set trees, clothes and wooden buildings alight.

The asteroid blamed for killing the dinosaurs was approximately 11 miles in diameter. Collision with an asteroid 300 miles in diameter would level everything manmade or alive on an Earth-sized planet.

Airblasts and fireballs: Anyone taking concussion damage from an airblast must roll vs. HT, at -1 per 5 points of damage, to avoid temporary or permanent deafness. Hearing loss lasts for 20-HT minutes, after which a HT roll is made to recover: use the Recovering from Crippling Injuries rule on B. 129.

Anyone seeing the fireball from a major meteor or comet impact must roll vs. HT for each eye to avoid being dazzled (sunglasses or anti-glare goggles give a +1 to +5 modifier). Blindness lasts for 20-HT minutes, after which a HT roll is made to recover: use the Recovering from Crippling Injuries rule on B. 129.

Table A: Falling/Flying Objects



Very light object, under 10 lbs; 1/4d damage. May be dodged or blocked.



Object weighing 11-20 lbs; 2d damage. May be dodged or blocked.



Object weighing 21-30 lbs; 4d damage. May be dodged or blocked.



Object weighing 31-90 lbs; 9d damage. May be dodged.



Object weighing 91-180 lbs; 6d × 3 damage. May be dodged.



Object weighing 181-600 lbs; 6d × 10 damage. May be dodged.



Object weighing 601-3000 lbs; 6d × 50 damage. May be dodged.

Table B: roll 1d. (See rules on p.B131)



Soft object (half crushing damage).



Hard object (full crushing damage).



Window glass or other sharp edge (full cutting damage)

Adventure Seeds

Indian Summer (Old West/Deadlands): The heroes have joined a posse to hunt down Walt "Death Valley" Davies, a stagecoach robber with a $500 bounty on his head.

Davies married a Apache girl, and his father-in-law is a powerful shaman. After tracking the outlaw for two days, the posse is hit by an unexpected severe hailstorm (doing 1d-2 damage per turn). Much of the posse turns back, leaving the PCs to go on alone. Crossing a narrow the next day, they're hit by a flash flood -- a surge of water higher than their heads, carrying a huge amount of debris. If they keep going after this, the shaman may have other tricks up his sleeve to protect his son-in-law: thunderstorms, tornadoes, or even worse.

Buried Treasure (Cliffhangers): It's 1932, and Prohibition is still in force. The PCs are smuggling cases of whisky from Canada to Alaska, when their truck is buried by an avalanche. Digging themselves out of the snow is the easy part; the hard part will be deciding whether to abandon 500 bottles of 90% proof whisky and walk to the next town in near-Arctic conditions, or to get drunk and hope to be rescued.

Shake, Rattle, and Roll (Cops/Voodoo): Mama Marie, a well-known mambo, has predicted that if rapper, initiate, and accused multiple murderer Jesus Valdez is executed, the city will be leveled by an earthquake before midnight. The heroes will have their hands full trying to keep the peace after Valdez's execution -- particularly when a Mercalli IX quake strikes the town, causing major panic, frenzied looting, and war between the societies and lodges.

An Ill Wind (Supers/Espionage): Dr Scales is an reclusive meteorologist and gadgeteer, widely thought to be mad because of his political views as well as his scientific theories. He's lived and worked alone on a small island (approx three miles across) in international waters in the Caribbean for years -- but the government has heard that he's giving sanctuary to terrorists, and sends the heroes in to investigate.

Scales has the ability to generate an intense hurricane around his island if he detects an attack -- fifty miles wide and 50,000' high, with a five-mile eye around his island. If the PCs can get through that, Scales will threaten to seed the hurricane with smallpox (see pp. CII172-173) and send it towards Cuba: first stop, Camp X-ray.

Hard Rain Gonna Fall (Space): Kimberly is a chilly moonless world in a system dominated by asteroid belts. Its temperate equatorial belt provides the belters with refineries and R&R, and its economy is booming. Belters have placed ion engines on a mile-long asteroid, to nudge it into orbit around Kimberly so that it may be used as an orbital starport (ultimately, part of a space elevator). Unfortunately, one of the engines explodes, killing the scientist who performed the calculations and causing the asteroid to break up. The heroes arrive in time to help the belters try to prevent any of the larger fragments striking near Kimberly's towns -- and nervous townspeople are desperate to be evacuated.


Article publication date: July 16, 2004

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