On 8 June IG reported a continuing high level of seismicity at Sierra Negra, characterized by a larger number and magnitude of earthquakes, indicating magma movement.
The number of events per day had been significantly increasing since mid-2016.
In the previous 10 days there was an average of 42 local events/day; on 25 May there were 104 events, the largest number of earthquakes per day recorded since 2015.
In addition, in a 24-hour period during 7-8 June there were a total of 48 volcano-tectonic events, two long-period events, and three hybrid earthquakes; a M 4.8 long-period earthquake was recorded at 0715 on 8 June.
The earthquake epicenters were mainly located on the edges of the crater, in two NE-SW trending lineaments; the first covered the N and W edges of the crater and the second went from the NE part around to the S edge.
Data showed very large deformation at the caldera?s center, compared with lower levels of deformation outside of the caldera.
Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)