A "swarm" of earthquakes that touched off Sunday morning in southern California was still rolling along Monday afternoon, registering more than 300 small to moderate quakes that could be felt from Arizona to San Diego. The swarm is unusual but not as rare as you might think.

During an earthquake swarm, an affected area experiences a rapid-fire series of temblors that are all similarly proportioned, so that no one shock emerges as the obvious source of the rest. According to Julie Dutton, a geophysicist with the U.S. Geological Survey, diffuse clusters like these are far less common than earthquakes that arrive as one big shake followed by a series of smaller aftershocks.

Dutton estimates that the USGS records about 30 to 40 notable swarms a year, compared with 20,000 to 30,000 total earthquakes. Because swarms are rooted in the same kind of plate movements and stresses that cause more traditional quakes, she thinks that a large part of the phenomenon's apparent scarcity is based on semantics.

Swarms "are really hard to characterize," she told Life's Little Mysteries. "It's all the same mechanisms. It's just a different way of finding equilibrium in the environment."

Where did the swarm start?

The current swarm originates just outside of the small farming town of Brawley, Calif., about 30 miles (45 km) north of the state's border with Mexico. According to Dutton, swarms with magnitude ranges close to the current one arrive in that area at the rate of one or two per decade, with the most recent one hitting in 2005.

The 2005 swarm, which topped out with a 5.1-magnitude event, was surpassed by yesterday's high of 5.5, the cut-off magnitude at which seismologists expect to start seeing casualties in developed countries, according to USGS geophysicist Paul Caruso. But there have been no reported injuries from the Brawley quakes, and Caruso said Monday morning saw a considerable slowing in the area's seismic activity.

Cyclone Beatrice struck northern Italy on Sunday, causing light flooding, storms and a mini-tornado but also providing much needed cooling after a weeks-long heatwave.

Farmers and vintners hampered by the drought looked forward to Beatrice, which succeeded Lucifer, an anticyclone with winds that spiral out from a high-pressure centre, which had brought hot air from the Sahara Desert.

The cyclone is expected to move slowly toward the south of Italy, lowering temperatures and causing storms next weekend.

Some roads and highways were flooded in the centre-north of the country, causing delays for Italians returning home from summer holidays.

A mini-tornado also ravaged the renowned botanical gardens of Villa Taranto on the shore of Lake Maggiore, uprooting 250 plants and destroying others at the arboretum visited by 150 000 people each year.

Officials say a strong earthquake has shaken a remote area of eastern Indonesia. The quake was located fairly deep below the northern Molucca Sea and no tsunami warning was issued.

The U.S. Geological Survey says the earthquake measured magnitude 6.4 and struck late Sunday. It says it was centered 138 kilometers (85 miles) west-northwest of the town of Tobelo at a depth of 70 kilometers (43 miles). The area is also south of the southern Philippines.

There were no immediate reports of damage or injuries from the remote area.

Indonesia straddles a series of fault lines that make it prone to volcanic and seismic activity.

A giant quake on Dec. 26, 2004, triggered a tsunami in the Indian Ocean that killed 230,000 people, half of them in Indonesia's Aceh province.

Parts of Maryland are still getting drenched. Thunderstorms dumped up to five to six inches of rain, making it one of the wettest days of 2012.

Derek Valcourt has more on the serious damage it caused.

The storm caused lots of localized flooding, some road closures, even some power outages, and one sinkhole in Baltimore just got a lot worse.

Cell phone cameras captured this funnel in the water off Cobb Island in Charles County during a tornado warning that set of sirens, but it was severe rains that did the real damage.

Scientists say Arctic sea ice is likely to shrink to its smallest recorded size sometime next week. The ongoing thaw has opened new sea lanes to shipping, with a Chinese icebreaker recently becoming the first ship to cross the Arctic Ocean from China to Iceland. Matt Stock reports.

Serbia evacuated thousands of villagers on Saturday and called in the army to help fight wildfires raging through the drought-hit western Balkans.

Fires near the southwestern Serbian town of Cacak swept through hillsides and cornfields dried to a crisp by scorching temperatures, forcing the evacuation of three villages, a Reuters correspondent reported.

"I've lost everything," said Mileta Cajic, from the village of Srezojevci. "An entire orchard, woods, raspberries, and now my house is about to go up in flames. This is the worst disaster one could imagine."

Russia sent a Beriev Be-200 fire-fighting plane, with a capacity of 12 tonnes, to join a Russian helicopter that has been in action for days trying to douse the fires.

Tens of thousands of Louisiana residents have been ordered to evacuate as Tropical Storm Isaac picks up strength in the Gulf of Mexico - and it may strike seven years to the day after Hurricane Katrina devastated the same area. More than 50,000 residents of the St. Charles Parish in southeast Louisiana have been told to leave ahead of Isaac, which is churning in the Gulf.

Governor Bobby Jindal suggested anyone in low-lying parts of the state's coastal parishes leave their homes, while evacuations were also enforced in the lower areas of the Alabama coast, which is likely to be lashed by rain, wind and flooding. Isaac is expected to crescendo to a Category 2 hurricane before striking land along the Gulf Coast by Tuesday night or Wednesday - the anniversary of Katrina - according to the National Hurricane Center.

Additional images

More earthquakes shook Imperial County overnight, part of a swarm of hundreds of temblors that has the region on edge. More damage was uncovered Sunday night, including about 20 mobile homes that suffered damage to their foundations. Photos show merchandise shaken from store shelves, and part of a home's terra-cotta roof collapsed.

A number of families were displaced and hospital patients evacuated as a result of a swarm of hundreds of earthquakes.

No deaths or critical injuries were reported as a result of the quakes, the largest of which measured magnitudes 5.3 and 5.5. There appeared to be fewer quakes overnight Monday compared with Sunday.

Some buildings were damaged by the earlier quakes, including 20 mobile homes that shifted from their foundations, according to the Imperial County Office of Emergency Services. The office was working with the American Red Cross to set up a shelter for displaced families at the Imperial Valley College gymnasium.

The quakes cause scattered power outages, including at Pioneers Memorial Hospital in Brawley, which lost power for about three hours. Assistant hospital administrator Art Mejia said generators immediately kicked in, but officials decided to evacuate patients as a precautionary measure in case the facility had suffered structural damage.

"We decided to err on the side of caution," he said.

Two wildfires in the south forced the evacuation of around 1,000 residents, making this the worst summer in a decade for countryside devoured by flames, authorities said Sunday.

A fire started near Bedar, 85 kilometres (about 50 miles) north of Almeria, where residents spent the night in a sports centre, regional officials said. Residents and army personnel have collaborated with firefighters in combating the flames, Bedar Mayor Maria Gonzalez said.

Another fire was being brought under control late Sunday near the Mediterranean beach resort of Estepona, about 35 kilometres (20 miles) west of Marbella.

This year, Spain has lost 149,300 hectares (577 square miles) of forest and countryside in more than 11,650 wildfires, compared to around 107,000 hectares (415 square miles) for the whole of 2002, according to official statistics.

Millions of residents in four vulnerable Gulf Coast states were bracing for the arrival of a powerful tropical storm that has already claimed several lives on its path through the Caribbean.

The governor of Florida, Rick Scott, declared a state of emergency ahead of tropical storm Isaac's expected landfall Sunday night in the Florida Keys, with the storm then expected to intensify into a 105mph hurricane as it moves north into the Gulf of Mexico and towards the Alabama-Mississippi-Louisiana coastline.

But with tropical storm-force winds extending up to 200 miles from Isaac's centre, the area under threat for moderate to substantial damage covered much of southern and western Florida and along the Gulf Coast to Louisiana.