Scientific files
 

Aftershocks of the Haiti earthquake of 12 January 2010 and associated ground deformation

Aftershocks of the earthquake:

The violent earthquake of magnitude Mw = 7.2 on 12 January 2010 at 21h53 UTC, which took place near Port-au-Prince, capital of Haiti (Figure 1), was followed by many aftershocks recorded as far away as the CEA network in metropolitan France (Figure 2).

Map of Haiti showing epicentres of the magnitude-7.2  earthquake of 12/01/2010  and the magnitude- 6.0 aftershock on 20/01/2010. The yellow and orange filled circles indicate  the historical seismicity, with fault zones also shown.
 Figure 1: Map of Haiti showing epicentres of the magnitude-7.2 earthquake of 12/01/2010 and the magnitude- 6.0 aftershock on 20/01/2010. The yellow and orange filled circles indicate the historical seismicity, with fault zones also shown.

Eight hours of seismic  recordings of stations used by the CEA/DASE. Note the main earthquake of  magnitude 7.2, the first 5 aftershocks within the next 2 hours, with their  magnitudes (greater than or equal to 4.7) as recorded by the network in  metropolitan France,  as well as the numerous other aftershocks that followed.
 Figure 2: Eight hours of seismic recordings of stations used by the CEA/DASE. Note the main earthquake of magnitude 7.2, the first 5 aftershocks within the next 2 hours, with their magnitudes (greater than or equal to 4.7) as recorded by the network in metropolitan France, as well as the numerous other aftershocks that followed.

Sixty-four of these aftershocks occurring up until 27 January 2010 were of magnitude 4 or greater, and could be felt by the population (source: EMSC for events of magnitude < 4.6). After 3 February 2010, no other aftershocks of magnitude 4 or greater were recorded on the network in metropolitan France (or in the database of the Euro-Mediterranean Seismological Centre). While the number of aftershocks fell to below 5 per day as of 14 January (Figure 3), these events nonetheless remained of strong magnitude (Figure 4), the most important shock (magnitude 6) taking place on 20/01/2010 at 11h03 UTC.

Number of aftershocks of magnitude 4 or greater recorded per day up until 03/02/2010 (source: EMSC for events of magnitude < 4.6). No event was detected in this range of magnitude between 27/01/2010 and 03/02/2010.
 Figure 3: Number of aftershocks of magnitude 4 or greater recorded per day up until 03/02/2010 (source: EMSC for events of magnitude < 4.6). No event was detected in this range of magnitude between 27/01/2010 and 03/02/2010.

Number of aftershocks of magnitude 4 or greater recorded between 12/01/2010 and 03/02/2010 (source: EMSC for events of magnitude < 4.6).
 Figure 4: Number of aftershocks of magnitude 4 or greater recorded between 12/01/2010 and 03/02/2010 (source: EMSC for events of magnitude < 4.6).


Study of ground displacements

A map of the displacements induced by the Haiti earthquake was established by comparing the geometries of two satellite images, taken before and after the earthquake, using an image correlator suitable for subpixelic measurements (Figure 5). (Reference: Van Puymbroeck, Michel, Binet, Avouac and Taboury (2000), Measuring earthquakes from Optical Satellite Images, Applied Optics, 39 (20), 1–14.).


 Figure 5: Map of surface displacements induced by the Haiti earthquake of 12 January 2010, measured using two SPOT5 THR images covering the event.

Given that the incidence angle of the images is 24°, this measurement includes a vertical displacement component in addition to the horizontal component (East-West and North-South). The map of East-West displacements shows that a zone located immediately North of the Enriquillo Plantain fault  has undergone a displacement of almost 2 m towards the West relative to the rest of the image. This displacement is compatible with sinistral slip along a ruptured segment of the Enriquillo Plantain fault; the eastern end of this rupture is represented in red on Figure 5.
Farther East, about 30 km from the rupture zone, surface displacements of a few millimetres can be observed around Port-au-Prince (Figure 6). The signal observed at the foot of the mountain massif does not seem to be of tectonic origin because it is too far away from the rupture. It could be induced by site effects.

Map showing surface displacements observed around Port-au-Prince. The ground deformation is probably induced by site effects.
 Figure 6: Map showing surface displacements observed around Port-au-Prince. The ground deformation is probably induced by site effects.
Haiti earthquake : East/West component Haiti earthquake : North/Sud component