[Webstral]

I think damage to San Francisco from the Richmond strike depends entirely on the altitude of the epicenter of the explosion. An airburst of almost any elevation over Richmond will break a lot of glass in North Beach, the Marina, and downtown. With a surface detonation, though, the shockwave and thermal pulse will run into the low hills on the western edge of Richmond I mentioned above. There will be plenty of turbulence in the air, to be sure. But damage from overpressure should be slight given the distance of northern San Francisco from the epicenter and the deflection of the pressure wave by the hills.

Deflection by the low hills at Point Richmond will not completely eliminate the effects of overpressure on North Beach or adjacent areas. However, we should bear in mind that the pressure drops from 20psi at 2.5km from the epicenter to 5 psi at somewhat less than 6km from the epicenter. It’s another 12km from the edge of that ring to North Beach. Pressure will drop as a function of the expansion of a hemisphere. If the overpressure at 6km (just keeping the math simple) is 5 psi, then the same force will be acting on a much larger surface area when the hemisphere expands to a radius of 18km. The surface area of a hemisphere with a radius of 6000m is slightly less than 118,000m2. The surface area of a hemisphere with a radius of 18,000m is 355,000m2. Keeping the math simple, this should mean a force 1/3 as great as when the hemisphere has a radius of 6km. These are all rounded figures, just for the sake of getting a decent approximation.

Another way of looking at the math (admittedly without my having a really good grasp of the geometry and physics involved) is to observe that the overpressure drops from 20 psi at 2km to 5 psi at 6km. The pressure decreases fourfold as the radius increases by a factor of 3. The radius of the hemisphere increases by just about a factor of 3 from the edge of the 5 psi ring to North Beach. While someone with real subject matter expertise could give precise figures, my back-of-the-envelope sketch shows that pressure drops to about 1.25 psi. This jibes tolerably with the above example, in which pressure drops from 5 psi to about 1.66 psi.

Since this pressure is applied very abruptly to glass facing towards the water in North Beach, one can expect a fair amount of broken glass—especially among the big picture windows facing in exactly the wrong direction.

Accounting for the impact of the Point Richmond hills on the pressure reaching North Beach is tougher. The pressure wave will be distorted as it goes over the hills and at least partially deflected. Once over open water, though, we might expect that portion of the shockwave that went over the hills to descend towards the water. This question addresses fluid mechanics, about which I know very, very little. I can’t say for certain that a ridge 100m high in Richmond would completely block the overpressure from the blast from striking 2 story houses in North Beach. Neither can I say that the pressure would be unaffected as a result of the pressure wave “spreading out”, as it were, to fill the gap below the 100m line and the surface of the water as the pressure wave moves southwest across San Francisco Bay. My guess is that there would be some reduction. I can’t say how much. Even a 50% reduction would very favorably affect survivability of residential structures in North Beach.

The thermal radiation, on the other hand, is much more straightforward. Infrared light moves in a straight line. There is a significant mass between the epicenter of the explosion in Castro Creek and North Beach. The effect of thermal radiation on North Beach should be zero to negligible.

I certainly agree that there would be troublesome fallout from the strikes. How much depends a good deal on how many airbursts versus ground bursts we’re talking about. My interpretation is that the three .5Mt strikes are airbursts, while the 1.5Mt strike is a ground burst. That last strike would put up a lot more irradiated dust than the other three combined. The water at the point of impact is only a couple of feet deep. The surface underneath the water is wet mud. I don’t know how deep that mud goes before one reaches bedrock. In any event, I think one could expect fallout in an arc from Modesto to Sacramento. This is unfortunate, given that there’s a lot of productive farmland everywhere in that arc. How widely dispersed the fallout is and how far inland it reaches depends on the weather, obviously. If everyone was very, very lucky the places most affected by fallout would be those places already burned to a cinder by the first round of strikes or basically uninhabited along the north shore of Suisun Bay. What really sucks is that some very productive and potentially defensible farmland on the islands of the Delta lies directly east of Richmond. The best case scenarios would be either heavy rain such that the fallout from the Richmond strike is knocked out of the air almost immediately and falls in central Contra Costa or high winds scatter the fallout across such a wide area that the agricultural areas of the Central Valley get a light dusting.

I put the major functional military bases on the islands for security purposes. I chose Alameda because the facilities already were there in 1997. The island would be comparatively easy to secure, freeing military manpower for other tasks. People useful to Milgov could be packed onto the island, where they would be manageable and relatively secure.

The hotness of Carquinez Strait is something I haven’t really thought about before. It certainly could be a real problem when it comes to exploiting the inland waterways. I’d be curious to see some numbers on how hot the shoreline would be after 500kt airbursts at the given locations. The lynchpin of Blue Two and of Sixth US Army operations in central California is free movement all along the inland waterways, from Alviso in the South Bay to the Golden Gate to the Petaluma and Napa Rivers, throughout the Delta, and upriver to Sacramento and Stockton. If Carquinez Strait is too hot to move through in 1998, a very serious dent is going to be put in my scheme.