This page is out of date; see our updated FAQ.

Frequently asked questions

Q: There are many earthquakes on your list at a depth of 10 km. What is so special of that depth?
A: One of the most difficult parameters to measure in real time is the focal depth of an earthquake. In many if not most cases the network geometry with respect to the epicenter does not allow a reliable depth determination. This is the case in particular for shallow earthquakes if no recordings from stations close to the epicenter are available. At the same time, in most parts of the world the earthquakes are shallow, i.e. within the Earth's crust. In cases where the depth determination is not possible and the earthquake hypocenter is most likely shallow, we assign a default depth of 10 km. This doesn't mean that the hypocenter depth really is at 10 km. Instead, it means a shallow hypocenter, where shallow usually means anywhere between the Earth's surface and 30-40 km depth. Note that at GEOFON often a manual revision of the location is performed for important earthquakes. In the manual revision an experienced seismologist can sometimes identify signals which help to constrain the depth better than the automated analysis can do. In that case, earthquakes with a depth initially set to 10 km can later be relocated at a different and better constrained depth.

Q: Your magnitude is 6.2 whereas in the media it was reported as 6.3. Why?
A: Besides the well-known Richter magnitude scale, several other magnitude scales exist which mostly differ in the way the magnitude is computed. Differences are not only due to uncertainties in the measurements, but may also reflect physical properties of the earthquake. Another reason for differences is the fact that magnitude accuracy improves as more data become available, which takes some time. Therefore, initial, quick estimates have relatively large uncertainties, whereas later measurements based on many more data are more reliable. In order to avoid confusions, many agencies stick to their initial estimates often for hours. At GEOFON, our goal is to provide the most accurate and current information available at any time, which might mean frequent updates of the magnitude especially in the first minutes following an earthquake.

Q: There was an earthquake on Eritrean territory but in your list the region is given as Ethiopia. Why?
A: Region names are always a politically sensitive issue. This is why in global earthquake monitoring the most commonly used naming scheme is that of the Flinn-Engdahl regions.

Q: What do these funny circles in the earthquake list mean?
A: These are so-called "beach balls" which are a common way to graphically show the focal mechanism of the earthquake. In combination with other geological information these "beach balls" give seismologists a hint about the geometry of the fault plane that ruptured during the earthquake. Determination of focal mechanisms is a relatively complicated and time consuming procedure. It also requires a high signal quality in the seismograms used. This is why we cannot provide focal mechanisms for every earthquake but rather concentrate on the largest events. This service was started in January 2011.

Q: There are letters 'A', 'C' and 'M' in the list. What do they mean?
A: Earthquake locations are published automatically without review by a geophysicist if the event was observed at least at 25 stations. While this usually ensures both decent location and magnitude, automatically determined earthquake locations may be erroneous, unless revised by a geophysicist! Automatic locations are therefore marked with a red A in the respective row. Manually revised locations are marked with a green M instead. Also, small events with less than 25 observations are always manual, because these events are published only after review. If an automatic solution was checked and found to be satisfactory without manual revision, it is shown as confirmed by the letter C.

Q: Access to my IP address appears to have been blocked. Why?
A: To find out, best contact GEOFON staff by e-mail. The most common reason is excessive use by accessing the earthquake list or the RSS feed every few seconds. Due to limited hardware resources we cannot tolerate this. It doesn't make sense anyway, because the list is updated only once per minute.