For the third time in a week, parts of Berks County were shaking Friday night.
The United States Geological Survey detected a 2.1-magnitude earthquake centered about 1.25 miles west southwest of Sinking Spring at 10:47 p.m. The quake was about 1.8 miles deep, according to USGS.
Officials at the Berks County Department of Emergency Services said they did not receive any reports of damage from the earthquake but did get some calls about the noise it created.
The quake was the third this week reported in Berks and the second near Sinking Spring since Sunday. A 1.5-magnitude quake was reported a few miles east southeast of Bernville in Penn Township at about 2 a.m. Friday. (The USGS updated the description of the location and magnitude from its first report.) And on Sunday a 1.7-magnitude quake was recorded at about 1:40 p.m. in the Sinking Spring area.
Its epicenter was in South Heidelberg Township, a little over 100 feet south of Penn Avenue and just west of Aspen Avenue.
The USGS received reports of Friday’s quake in South Heidelberg, Sinking Spring, Reading and Mohnton, among other places. It was also felt as far away as Schuylkill Haven, according to the USGS.
Berks has a history of reported earthquakes over the last half-century.
Hundreds of fault lines cross through Berks County, including one that intersects with Penn Avenue just east of where Friday’s earthquake struck. In an interview with the Reading Eagle in 2018, Dr. Edward Simpson, a professor of geology at Kutztown University and chairman of the school’s physical science department, explained why the region is so prone to small quakes.
He said this area has gone through four mountain-building phases dating back to the Triassic Period. All that geological tumult has left the rock buried beneath Berks filled with tons of small fault lines.
“It’s riddled with them,” Simpson said.
The faults vary in age and size, he said, which means there’s frequent readjusting and crumbling going on. That’s not uncommon, Simpson said, with somewhere around 130,000 tiny earthquakes happening around the world each day.
Of course, in most cases they’re too small for anyone to notice.
What leads to the quakes is a mixture of circumstances, Simpson said. Part of it is the makeup of the rock, with crystalline rock like the limestone that cuts through the county particularly prone to breaking.
There’s also water, which can work as a lubricant to allow shifting and create added pressure. Simpson said that when the water table rises significantly, water fills the tiny pores usually occupied by air. That adds extra weight and can increase the already immense pressure the rock is under.
Magnitude vs. intensity
Friday’s earthquake measured as a IV on the Mercalli Intensity Scale. While magnitude and intensity are similar — high magnitude equals high intensity — they each measure different characteristics of earthquakes.
Magnitude measures the energy released at the source of the earthquake, while intensity measures the strength of shaking produced by the earthquake at a certain location.
Magnitude is determined from measurements on seismographs. Intensity is determined from effects on people, human structures and the natural environment.
A IV-level earthquake, according to the intensity scale, is typically felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors can be disturbed; walls make a cracking sound.
Source: Berkshire mont