The seismic waves would have been monitored over the entire Earth. Our seismograph recorded a very strong signal here in Colorado for example. The National Earthquake Information Center in Golden, Colorado reported that the earthquake today in Turkey registered a 7.8 on the Richter scale. However, another report stated that Turkish authorities measured the earthquake at 6.8. There are often discrepancies between magnitudes assigned by different agencies because they measure the seismic waves with different instruments.
Some magnitudes describe the level of high frequency energy.
Some describe the level of low frequency energy. We are still not able to predict quakes in the sense of anticipating the time and place and size of an earthquake. There has not been much improvement on the prediction front. An earthquake of this size will normally produce many aftershocks. Most of these will be small, but some could be large enough to produce additional damage.