  People use Online Social Media to make sense of crisis events. A pandemic
crisis like the Covid-19 outbreak is a complex event, involving numerous
aspects of the social life on multiple temporal scales. Focusing on the Spanish
Twittersphere, we characterized users activity behaviour across the different
phases of the Covid-19 first wave.
  Firstly, we analyzed a sample of timelines of different classes of users from
the Spanish Twittersphere in terms of their propensity to produce new
information or to amplify information produced by others. Secondly, by
performing stepwise segmented regression analysis and Bayesian switchpoint
analysis, we looked for a possible behavioral footprint of the crisis in the
statistics of users' activity.
  We observed that generic Spanish Twitter users and journalists experienced an
abrupt increment of their tweeting activity between March 9 and March 14, in
coincidence with control measures being announced by regional and State level
authorities. However, they displayed a stable proportion of retweets before and
after the switching point.
  On the contrary, politicians represented an exception, being the only class
of users not experimenting this abrupt change and following a completely
endogenous dynamics determined by institutional agenda. On the one hand, they
did not increment their overall activity, displaying instead a slight decrease.
On the other hand, in times of crisis, politicians tended to strengthen their
propensity to amplify information rather than produce it.
