We purchased the house about 2 years ago. The house is about 50 years old. Today we removed the carpet and the hardwood floors under the carpet. We found out the slab has an approximately 10ft long crack. See the picture. The crack goes from hairline and branches off to bigger cracks. See photo. It's about 5 inches deep from what I could measure.
The house is in Granada Hills, California. I was thinking it's maybe due to earthquakes or earth shifting. I know a major earthquake happened in 1994. The walls appears to be fine and show no sign of structural damage.
What type of crack is this? How can I fix it and should I be concerned? Should I use cement, Emecole 555 or a bottle of concrete filler? Any help or insight would be appreciated.