Today was a shaky day in Northern California because of a big earthquake near the Nevada border.

I had a busy morning, including attending a meeting during my lunch hour. This afternoon I decided to take a quick nap. I set the timer on my phone for 10 minutes and stretched out on the couch. About five minutes later I was woken up by the quake.

I could feel myself being rocked back and forth after the initial shock that woke me up. I looked over at the overhead lamp in the dining room and it was swaying back and forth.

My first thought was that it was a quake in the Bay Area and I knew that if I felt it that strong it would be a big one.

I quickly checked my phone to get details about the earthquake and it initially said that the quake was about 20 miles away and was a 4.8. It listed a larger quake farther away at 5.9 at about the same time.

Later the 4.8 quake was removed from the list after being reviewed by a seismologist. Sometimes the algorithm that evaluates sensor data gets confused so there is always a disclaimer if it has not been reviewed by a person.

A friend of mine who lives in Stockton felt it much more than I did, so I though it might have been correct.

The Shake Map shows that the earthquake was felt over a large area. The reason why it was felt in such a large area was because it was a very strong quake, and also because the ground is very solid in the area which perpetuates the waves from the earthquake much better.

The initial earthquake was later updated to 6.0 and there have been multiple aftershocks with a 5.2 being the largest and also two at 4.6.

There have now been almost 80 aftershocks including 6 within the last hour.

The first quake was in the Little Antelope Valley along a fault which is part of the Antelope Valley fault zone. There is often some activity further north in the Nevada section of the zone, but nothing like what we have today.

It will be interesting to see how long the aftershocks last. The last aftershock was a 3.7 about 10 minutes ago and there was a 4.3 about 40 minutes ago so they are still fairly strong. There is also about a 20% possibility that the 6.0 was a fore-shock so we may feel an even bigger shock later if it is.

Hopefully I will not be woken up in the middle of the night with the room shaking. If so, it will not be the first time as I have experienced several quakes in the middle of the night in Tokyo. It is definitely a weird feeling to wake up to a swaying room. Just like today from my nap.

Steven

• images are clips from the USGS website.