Last week's catastrophic earthquake in Japan -- on the heels of three recent tremblers in Haiti, Chile and New Zealand -- has highlighted the potential for similar destruction in the United States, where, under one scenario, downtown Los Angeles would be leveled.
"Let's say we have an 8.0 earthquake -- smaller than the one that hit Japan -- right on the San Andreas Fault," theoretical physicist Michio Kaku said on "Good Morning America" today.
"According to the U.S. Geological Survey, the devastation would be catastrophic. Downtown L.A. flattened. Forty percent could withstand an 8.0 earthquake, but 15 percent of the tall buildings are at risk and could, in fact, collapse."
An earthquake off the coast would present different challenges, he said.
"The potential here is that within a few minutes to five hours, a wall of water, 15-feet tall, could hit Los Angeles and go two to three miles inland," Kaku of the City College of New York said.
Experts predict that such a wave could travel from its point of origin at 500 miles per hour, hitting the beaches at about 30 miles per hour.
The United States has thousands of miles of coast line and many fault lines, especially on the West Coast. Among the concerns for experts is that a 9.0 earthquake could hit around the Aleutian Islands off the Alaska coast, or off the Pacific Coast.
Earthquake experts say a 9.0-magnitude quake on the San Andreas Fault, which runs through California, is impossible. The maximum magnitude, according to their estimates, is about an 8.0, which could still be devastating.
Only structures built since 1980 are up to the strictest of building codes, and the United States is not as well prepared as the Japanese are in terms of earthquake and tsunami protection, some experts say.
"The Japanese are the world's best in terms of preparing for earthquakes, and look what happened to Kobe," Kaku said, citing the 1995 Japanese earthquake that killed about 6,500 people. "Look what happened [last week] to Sendai, and look at the casualties in Los Angeles [if an 8.0 earthquake occurs]: 3,000 dead, up to 50,000 injured and the fires; 6,000 to 7,000 fires, raging fires out of control.
"Remember San Francisco in 1906, my grandfather witnessed it. Fires caused more damage than the earthquake itself."
San Francisco burned to the ground after a 1906 earthquake that is thought to have been a magnitude of 7.9.
Nowadays, to the south, after an undersea earthquake off the West Coast, "L.A. harbor would perhaps experience the worst damage in the case of a tsunami. ... Santa Monica, believe it or not, would not experience as much damage because of the geometry but Orange County, Newport Beach, Seal Beach, Huntington Beach, would also sustain massive flooding," Kaku said.
Much of the Los Angeles-area coast is protected by cliffs, so the tsunami would not penetrate into downtown L.A., Kaku said. But beach areas would be at high risk.
Santa Monica Beach would also be inundated, with a wave penetrating about half a mile inland. If a tsunami occurred during the summer, hundreds of thousands of people could be endangered.
"We're talking about whole areas being flooded. Some of these areas are very wealthy and they're very vulnerable," Kaku said. "I wouldn't buy beach-front property there."
To find out how you can help with disaster relief in Japan, click here.