The document summarizes seismic activity in northern Chile between May 5-12, 2020. It identifies three earthquakes above magnitude 5, including one near the coast of northern Chile of magnitude 5.1. The area has experienced large earthquakes in the past due to the subduction of the Nazca plate beneath the South American plate. The recent earthquake may be a foreshock as the curved subduction zone creates barriers that can segment megathrust quakes. Continued seismic monitoring is needed to understand future earthquake potential.

1. SEISMICITY OF THE WEEK
Computational Seismology Laboratory
Kaushik Kumar Pradhan
18th
May 2020
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2. OUTLINE OF THE PRESENTATION
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Section 1 - List of Earthquakes between 5th
May 2020 to 12th
May 2020
Origin time, region, magnitude, location and depth
Section 2 - Earthquake of Interest
Source properties and reason for selection
Section 3 - Seismotectonics of the Area
Detailed structure, tectonics and past earthquakes
Section 4 - Explanation for the event
Relationship between seismotectonics and the event

3. 3
SECTION 1 - LIST OF EARTHQUAKES (Mw
> 5.0)
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4. 4
TABULATED - LIST OF EARTHQUAKES
Google Sheet -
https://docs.google.com/spreadsheets/d/13kPjOJVgsfJA40L9n2Z0iFGFAayf0TrQ628tp69kB
O4/edit?usp=sharing
Time Latitude Longitude Depth/km Magnitude EventLocationName
2020-05-10T18:04:22 -22.7535 -68.1578 117.94 5.5 NORTHERN CHILE
2020-05-08T22:42:06 -23.2277 -68.8371 84.86 5 NORTHERN CHILE
2020-05-06T15:43:12 -19.3548 -70.4824 63.51 5.1
NEAR COAST OF
NORTHERN CHILE

5. 5
SECTION 2 - EARTHQUAKE OF INTEREST
(Hayesetal.,2013)
IRISandGoogleEarth
Northern Chile
Near Coast Northern Chile

6. 6
SOURCE PROPERTIES (North Chile Earthquake - 5.5)
USGS

7. 7
SOURCE PROPERTIES (North Chile Earthquake - 5.0)
USGS

8. 8
SECTION 3 - SEISMOTECTONICS OF THE AREA
Google Images
● South American arc extends over 7000 km.
● Plate boundary between Nazca Plate and the South
American plate.
● Relative to a fixed South American plate, Nazca plate
moves slightly northwards of east with velocity varying
from 65 mm year-1
to 80 mm year-1
.
● Since 1900, numerous magnitude 8 or larger
earthquakes have occurred.

9. 9
SEISMIC GAP OF NORTHERN CHILE
● Seismic gap - lack of recent seismicity in comparison
with other portions of a fault.
● Recorded earthquakes in Northern Chile region - M~8.8
event in 1877 and M 8.2 on 1 April 2014.
● Based on moment deficit calculations, indicate that this
was not the earthquake that had been anticipated.
● The earthquake sequence spans a section of the
subduction zone about one-third of the size of the
inferred 1877 rupture.
● Megathrust earthquakes is likely to occur to the south
and potentially to the north of the 2014 Iquique
sequence. Hayes, G., Herman, M., Barnhart, W. et al. (2014)

10. 10
BARRIER FOR PROPAGATION
Contreras-Reyes, E., Jara, J., Grevemeyer, I. et al. (2012)
● Abrupt increase in the dip from 10 degree to 22 degree.
○ Change in dip acted as a barrier for the propagation.
○ Subduction megathrust is not only segmented along the trench, but also in the
direction of the dip.
○ Large magnitude earthquake should cross the barrier, nucleated at depth more
than 20km.
● Curve section of Andean subduction zone plays important role in plate locking.

11. 11
SECTION 4 - EXPLANATION FOR THE EVENT
Hayes, G., Herman, M., Barnhart, W. et al. (2014)
● Earthquake in the northern Chile - Fold- thrust- belt
● M >3.5 earthquakes occurred offshore of Iquique between
August 2013 and March 2014, a 950% increase in the rate
from January to July 2013.
● Beginning on 16 March with a M 6.7 earthquake, the
foreshock sequence generated more than 80 M ≥4
earthquakes
● Earthquake near coast of northern chile - Just north of 2014
earthquake and might be a foreshock for a megathrust quake.
● In contrast to Iquique, Maule did not have any recognized
foreshocks. Its mainshock nucleated in the middle of the
South Central Chile Seismic Gap

12. 12
MOMENT DEFICIT ALONG NORTHERN CHILE REGION (Since 1900)
● The highly coupled section of the subduction zone ∼50–80 km to the south of the 2014 events, and the
moderately coupled interface for a similar distance to the north, have been positively stressed by the
2014 Iquique sequence.
● Given that earthquakes in this subduction zone have occurred in response to stress transfer in the past,
there is now an increased probability of megathrust earthquakes occurring to the south or north of the
April 2014 events in the future.
● Red - Moment for historical earthquake
● Dark blue - 2014 seismicity upto 3 April
● Light blue - Since 3 April 2014
● Green - summed moment
● Horizontal dashed line - moment accumulation
given coupling percentage
Hayes, G., Herman, M., Barnhart, W. et al. (2014)

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REFERENCES
Gavin P. Hayes, Eric Bergman, Kendra L. Johnson, Harley M. Benz, Lucy Brown, Anne S. Meltzer, Seismotectonic framework of
the 2010 February 27 Mw
8.8 Maule, Chile earthquake sequence, Geophysical Journal International, Volume 195, Issue 2,
November, 2013, Pages 1034–1051, https://doi.org/10.1093/gji/ggt238
Contreras-Reyes, E., Jara, J., Grevemeyer, I. et al. Abrupt change in the dip of the subducting plate beneath north Chile. Nature
Geosci 5, 342–345 (2012). https://doi.org/10.1038/ngeo1447
Hayes, G., Herman, M., Barnhart, W. et al. Continuing megathrust earthquake potential in Chile after the 2014 Iquique
earthquake. Nature 512, 295–298 (2014). https://doi.org/10.1038/nature13677
Shrivastava, M.N., González, G., Moreno, M. et al. Earthquake segmentation in northern Chile correlates with curved plate
geometry. Sci Rep 9, 4403 (2019). https://doi.org/10.1038/s41598-019-40282-6
M. Métois, A. Socquet, C. Vigny, D. Carrizo, S. Peyrat, A. Delorme, E. Maureira, M.-C. Valderas-Bermejo, I. Ortega, Revisiting the
North Chile seismic gap segmentation using GPS-derived interseismic coupling, Geophysical Journal International, Volume 194,
Issue 3, 1 September 2013, Pages 1283–1294, https://doi.org/10.1093/gji/ggt183