The earthquakes were moderate compared to what California is capable of producing. However, how do Downtowners who work on the upper floors of some of the area's tallest buildings react when a quake hits?
James Boyajian, an attorney who works on the 24th floor of the KPMG building, described last night's earthquake as "a joke" and this morning's as "a wave."
"Any earthquake under magnitude 5 is better than coffee, it wakes you up," he said, laughing at the idea of being afraid of the tremors.
Apathy about earthquake dangers was the common reaction from the Downtowners whom Blogdowntown interviewed.
Gary Conrad, who works on the 37th floor of 707 Wilshire Boulevard and also lives in Downtown, said he did not feel a thing last night or this morning. He explained that his building's routine earthquake and fire drills help ease his fears about an imminent, "Big one."
"I'm more concerned about getting hit by one of these cars," he said, gesturing to the busy street.
Sara Malkani, who felt this morning's tremor from her ninth-floor office on 6th and Flower Streets, said her building has emergency protocols in the event of an earthquake -- get under a desk or table. She said she didn't put much thought into any emergencies that could have resulted from the quake.
"I don't really worry about big earthquakes because it's one of those things we have no control over," she said.
Experts said the cluster of earthquakes that began Tuesday night are far from out of the ordinary for Southern California, but that the region has not seen this type of sequence in a few years.
At a news conference Wednesday morning, Kate Hutton of the U.S. Geological Survey at Caltech said there had been at least 30 quakes since Tuesday night, but only three could be felt by residents. She said officials are studying the quakes to understand whether it was a swarm or some other type of pattern.
"This is all part of the same earthquake sequence; they're all in the same area,'' Hutton told reporters at the briefing. "We haven't had anything in the L.A. Basin in the last few years, but that doesn't mean we're totally quiet, and we certainly have been active in the southern part of the state,'' she added.
The quakes jolted residents but caused no major damage.
"It shook us pretty good. We’ve felt earthquakes before, so it came as no surprise,” said Chris Nordyke, director of marketing at the Richard Nixon Library and Birthplace in Yorba Linda. “It shook open the door but nothing fell off the shelves.”
He said an inspection of the facility is underway.
Law enforcement officials in Orange County said there were no immediate reports of damage from the earthquake that hit near Yorba Linda about 9:30 a.m. (The Wednesday morning quake was initially downgraded to 4.1 but then upgraded back to 4.5.)
Lt. Santo Porto of the Brea Police Department, which serves that city and Yorba Linda, said police had evacuated the department to check the structure but found no problems. “There’s no damage in either city that we’ve heard so far,” he said.
Orange County sheriff’s officials said they had received no initial damage reports, either.
The series of quakes — including the 4.5 quake Wednesday morning and 4.4 quake Tuesday night — has rattled residents in the area.
“No one really freaked but everyone sure felt it,” said Roxann Reeves, supervisor at a Starbucks on Yorba Linda Boulevard, where about 20 customers were in line when the aftershock hit. “We’d all just been talking about the one last night.”
The first earthquake hit near Yorba Linda at 11:23 p.m. Tuesday; the second — upgraded from an initial magnitude of 2.2 — followed about a minute later, according to data from the U.S. Geological Survey. About a dozen aftershocks ranging from magnitudes of 1.2 to 2.2 rumbled the same area until about 3 a.m. Wednesday.
Well-known Scottish scientist Iain Stewart delivered that grim prediction yesterday in Brisbane during an address to a global geology conference.
Professor Stewart, a geologist and academic who has gained fame for multiple BBC television series on the planet, said the risk of disaster has grown because a growing number of mega-cities are built on or near major earthquake faults.
Large settlements since antiquity have been based on these fault lines because they also help provide water and are usually located near flat plains ideally suited for growing crops.
This "fatal attraction" to dangerous areas was "actually a good thing", because historically the trade-off was worth it since earthquakes were rare and most cities were not that large, he said.
While earthquakes today were often less destructive because of improved building codes, more people were affected because cities were larger, Prof Stewart told delegates at the 34th International Geological Congress.