What happened?
JOHANNESBURG, July 13 (Ridgecrest Online) — The U.S. Geological Survey said a preliminary earthquake struck Monday morning near Johannesburg in eastern Kern County at about 9:40 a.m. PDT. The agency placed the epicenter about 18 kilometers, or 11 miles, west-southwest of Johannesburg in the Indian Wells Valley region and said the quake was about 7 kilometers, or 4.3 miles, deep.
Why did some reports say 4.1 and others say 4.3?
Because the earthquake report was still preliminary. In the first hours after the shaking, the USGS listed the event as magnitude 4.3 on its website and 4.1 in a social post. That kind of difference can happen while scientists review more seismic data and refine the estimate.
This is a live agency report, not a journal study, so peer review is not part of the process.
How strong was it?
A quake in the magnitude 4 range is often felt over a wide area, but it does not always cause major damage. In the first reports, the USGS did not list injuries or damage from the Johannesburg-area quake.
The USGS also said shake reports suggested light to moderate shaking in parts of Kern and San Bernardino counties, with reports reaching farther into Los Angeles, Orange and Riverside counties.
Did people get warning?
Yes. The USGS ShakeAlert early warning system was activated, and some areas received alerts.
Why does this area keep showing up in quake reports?
Eastern Kern County sits in a seismically active part of Southern California, so smaller and moderate quakes are not unusual there. The USGS also reported a magnitude 4.2 quake near Frazier Park on Sunday, making Monday’s event the second magnitude-4-or-greater earthquake in Southern California in about 48 hours.
A separate June 1 Johannesburg-area quake shows how early numbers can change. The USGS first listed that event at magnitude 3.8 and later upgraded it to 4.1, while its online felt-report system logged 46 reports from people who felt weak shaking.
What should readers take away?
The main point is that the Monday morning quake was real, it was centered near Johannesburg, and the first magnitude estimate was still being checked. For earthquakes, the first number is often the best early estimate, not the final one.
