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First mainshock (Mw 8.1, April 1):
Epicentre located offshore northern Chile (Tarapaca region), offshore Pisagua, between Iquique and Arica (about 100 km NW of Iquique and about 150 km SW of Arica). The earthquake occurred at 23H 46min UTC on April 01.
This event should correspond to an inter-plate subduction earthquake, corresponding to the underthrusting of the oceanic Nazca plate under South America (located at the contact between the two plates).
Given the magnitude, focal mechanism, and relatively shallow depth, a moderate tsunami was generated. After NOAA, the maximum wave height was 2m along the coast of northern-Chile, in particular at Pisagua and Iquique.
Second large earthquake (Mw 7.6, April 3):
Epicentre located about 50km to the SW of Iquique, i.e. approximately 100km more to the South than the first mainshock of Mw 8.1. The event should also correspond to an inter-plate subduction earthquake, corresponding to the underthrusting of the oceanic Nazca plate under South America (located at the contact between the two plates). It can be seen as triggered by the first mainshock.
A small size tsunami was generated, with maximum wave height of 0.7m at Iquique and Patache (NOAA).
These earthquakes occurred inside the "northern Chile seismic gap" where many groups are working, in particular French and German teams, in association with Chile. The joint laboratory France - Chile LIA Montessus de Ballore (CNRS/INSU) is directly concerned.
Link to the IPGP special page:
http://www.ipgp.fr/pages/040121.php
============= INFORMATION ABOUT POST-SEISMIC RESPONSE =================
Matériel disponible en France pour un intervention:
GPS:
02/04/14 : Parc mobile GPS INSU : a priori environ 11 stations disponibles. Personnel du parc présent à la DT demain.
SISMO:
02/04/14: Parc mobile SISMOB INSU: only a few stations available (max 6). If strongly needed, some material may be retrieved from the field of other campaigns. No decision taken on April 2.
April 2, 14h40 (FR): Posted by Sergio RUIZ (DGF Chile)
Now, we had 10 stations of task force installed during the last week (fortunatly) more the PB stations. The first team is going to north to install other ten stations. I going tomorrow with other ten stations. Then, I hope that in a few days we will have installed 40 stations (trillium compact of 120 sec. more Quanterra digitizer).
The idea is that all data will be available.
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April 2, 16H03 (FR): Posted by Sebastian Hainzl (GFZ Potsdam, Germany)
GFZ is currently preparing a field response mission with around 20-30 seismic stations. GFZ is a partner of the IPOC (Integrated Plate boundary Observatory Chile) which is a European-South American network of institutions and scientists organizing and operating a distributed system of instruments since several years exactly in this region (see informations on http://www.ipoc-network.org/). Main partners of IPOC are besides GFZ, Institut de Physique du Globe Paris (IPGP), Universidad de Chile (Santiago, Chile), and Universidad Católica del Norte (Antofagasto, Chile). To my knowledge, the Chilean partners are also planning to install 20-30 additional stations. If you are also interested to join this mission, please coordinate your activities with Sergio Barrientos (Centro Sismológico Nacional de la
Universidad de Chile, CSN), sbarrien@dgf.uchile.cl who will coordinate the overall employment. The GFZ coordinator of this mission will be Günter Asch (asch@gfz-potsdam.de).
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April 2, 17H08 (FR): Posted by Christophe Vigny (ENS Paris)
Contribution to the GPS post-seismic campaign:
Two French colleagues (Emilie Klein (PhD student ENS) and Arthur Delorme (engineer IPGP) are presently in Chile.
They have with them about 20 GPS receivers. They may stay in Chile one more week to renew measures
on campaign GPS points in northern Chile.
A coseismic solution should be computed soon at IPGP/ENS (Jean-Bernard de Chabalier) using the RINEX data of 2010, 2012, and
the new 2014 measurements.
Marcos Morenno is likely to come soon to northern Chile to make a new measurement of GPS points
previously measured in march 2014 in the region.
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April 2, 18H35 (FR): Posted by Mohamed Chlieh (Geoazur - IRD, based in Peru)
Possible contribution to the GPS post-seismic campaign:
Du côté de Lima, l'IRD met à disposition un véhicule 4x4 et nous avons une équipe prête à intervenir si les collègues Chiliens le souhaitent. Nous avons aussi 5 à 7 stations GPS qui peuvent être mises à disposition si nécessaire.
Je suis en discussion avec les collègues de l'Institut de Geophysique du Pérou pour aller vider des stations permanentes qui existent dans le sud du Pérou. On peut dans la fouler venir donner un coup de main au nord Chili.
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April 2, 18H41 (FR): Posted by Christophe Vigny (ENS Paris)
About the GPS post-seismic campaign:
Francisco Ortega et Daniel Carrizo (au Chili) montent une intervention dont l'un des volets consiste à re-mesurer les réseaux de marqueurs GPS. ils disposent de matériel et de bras. ils nous informeront de ce qui leur manque et de quelle manière ils souhaitent solliciter tel ou tel partenaire pour une contribution.
April 2, 21H47 (FR): information posted by Christophe Vigny (ENS Paris)
About the GPS post-seismic campaign:
The Chilean team wishes to measure again about 60 GPS points in northern Chile, over a wide area extending beyond the rupture zone
of the April 1 mainshock, with the idea that an incoming great earthquake may be in preparation and could occur soon.
Of course the postseismic deformation of the April 1 mainshock is also a target.
They could also install some semi-permanent stations, to complement the cGPS network (continuous recording).
Chilean colleagues have like twenty Ashtech Net-R9 receivers to make these new measures, so that they would be greatly helped by the
fifteen ZX receivers of the french GPS pool presently in Chile together with the manpower of Emilie Klein and Arthur Delorme
that would stay one more week in Chile.
April 3, 08H47 (FR): information posted by Christophe Vigny (ENS Paris)
Chilean colleagues, Francisco Ortega and Daniel Carrizo, are taking charge of organizing the GPS survey in northen Chile, within the whole seismic gap associated with the 1877 (Mw ~8.8) earthquake. They call for an overall coordination of all interested foreign teams. The french colleagues Emilie Klein and Arthur Delorme (and the 20 Ashtech reveivers they have at hand) will integrate this collaborative survey according to the planing of the Chilean colleagues.
Since Daniel Carrizo contributed largely to the GPS measurements in 2010 and 2012 with the french team, he will organize the renewed measurement of the joint french - chilean GPS campaing profiles and network.
GPS receivers operated by the chilean team will have two buffers, 1Hz and 30 seconds. The 1Hz setting will require more filed work to retrieve the data.
The chilean colleagues willl support their own financial expenses, but they cannot support foreign colleagues that would have their own logistic (that would work in the field independently from the chilean teams).
April 3, 18H44 (FR): information posted by Jean-Pierre Vilotte (IPGP Paris)
French colleagues of IPGP are evaluating what is precisely needed on the field for seismology, knowing that the Chilean group moved fast with a large number of stations (~50) to complement the existing network, and that the German group will also install stations (~30). It is likely that the broadband network will be globally dense enough, but additional strong-motion instruments may still be needed, and maybe manpower in the field.
A mission will probably be organized from France to collect the data from two permanent stations (IPOC network) which could not transmit their data, and to repair what needs to be repaired.
An OBS survey is in the phase to be organized by GFZ and GEOMAR (Germany), probably with the Chileans colleagues. Are French teams working with OBSes interested in going to Chile ?
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April 4, information from Wayne Crawford (IPGP) and Audrey Galvé (Géoazur):
At the present date, most OBS stations are scheduled for other deployment. Only a few broadband OBSes could be available at IPGP
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April 5-6, information from Jaime Campos and Jean-Pierre Vilotte:
The post-seismic response in seismology is coordinated in the field by Sergio Ruiz and Diana Comte. Chilean colleagues will confirm their need very soon, but they are already thinking that any help to densify the seismological network and provide man power would be welcome.
From the French side, at least two persons from IPGP will travel to northern Chile to visit the french stations of the IPOC network and retrieve some data, including those of the remaining ILN stations (installed by Monika Sobiesiak, Germany).
IRIS (Suzan Beck, USA) is planing also a post-seismic response in Chile, likely concentrated in the most northern part of Chile and southern Peru (Arica elbow).
Above: Map of permanent stations in northern Chile (IPOC network). IPGP and GFZ sites have double sensors, broadband and accelerometer.
Above: Map of the seismological network in the rupture zone of the two April mainshocks. Green triangles, temporary stations installed by Diana Comte. Red squares: permanent stations.
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April 7, information from Guenter Asch (GFZ)
Today 14 recorders from GFZ (Trillium compact, Cube) arrived at Santiago airport. After customs clearance they will be sent immediately to Antofagasta.
From GFZ two persons will follow tomorrow and together with 3 persons from Chile, and will start to condense the IPOC network in the central part. Sergio Barrientos announced to sent the coordinates of the already installed and planned sites, deployed during the last days by the SSN. GFZ deployment will depend on these data, to form a joined and common network. At the moment, these additional stations are planed for one year. 10 more stations will be ready for shipment hopefully next week, so in total there will be 24 stations from GFZ. Finally, 2 more strong motions (ETNA) will be deployed permanently.
Besides the seismological part, a GPS group of 6 peoplefrom GFZ will remeasure about 50 points in the North, which have been visited
last time in March. They also will install 2 new continuous and permanent GPS sites.
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April 9, information from Jean-Pierre Vilotte (IPGP):
The chilean team has installed 26 new broadband stations in northern Chile, completing the permanent network, the 5 ILN stations from Germany already present in the Iquique region, and the 10 temporary stations that Diana Comte had installed before the Mw 8.1 first mainshock.
Considering that this represents overall a large and dense network, with many stand-alone stations (nor telemetred) that will require large amount of field work to retrieve the data every 1-2 months, it was decided between the Chileans and Frenchs that France will not install additional stations but will provide help (man power) to retrieve the data. A first mission from France will go to the field to help the chilean colleagues within the next week, and other teams (4 persons) will do the same probably in July and September. They mau help also to install strong-motions to complete the deployement in the seismic gap(s) of northen Chile if the Seismological Service of the UChile can obtain some of such instruments from the Engeneer group.
The last information from the US (Susan Beck) indicate that they may finally not organize a field response in seismology.
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================ Earthquake DATA first mainshock Mw 8.1 ===================
Localisation EMSC:
Region OFFSHORE TARAPACA, CHILE
Date time 2014-04-01 23:46:49.0 UTC
Location 19.72 S ; 70.86 W
Depth 33 km
Localisation DGF Chile:
Hora UTC 23:46:45 01/04/2014
Latitud -19.572
Longitud -70.908
Profundidad 38.9 Km
Moment magnitude, focal mechanism, and depth from waveform inversions:
Comment: the expected rupture plane is the low angle east-dipping plane, with almost pure thrust faulting.
Lien vers la page de GEOSCOPE/IPGP sur la source du séisme, posted by Vincent Douet:
http://geoscope.ipgp.fr/index.php/fr/catalogue/description-d-un-seisme?seis=usc000nzvd
TSUNAMI (NOAA):
Summary: End of tsunami warning for the Pacific at 04h42 UTC. Tsunami height has been measured up to 2m along northern Chile (Iquique, Pisagua).
(see end of this section for more details about the tsunami)
------------------------------------------------------------- INFORMATIONS ABOUT THE CONTEXT OF THE EARTHQUAKE ----------------------------------
April 2, 09h10 (FR), posted by Raul Madariaga:
Le tremblement de terre d'Iquique de Mw 8.2 arrive à la fin d'une cascade de sismicité qui s'est propagée au large d'Iquique vers le Nord depuis le 16 Mars. Avec Sergio Ruiz, Amaya Fuenzalida, Marianne Métois et Christophe Vigny Nous avons beaucoup travaillé sur ce qui est maintenant approprié appeler des précurseurs.
Map showing the April 01 mainshock (Mw 8.1) and early aftershocks in brown (till 06H UTC). "Precursors" (foreshocks) as color circles.
(circles = epicenters) Map produced by Raul Madariaga.
April 2, 9h15 (FR): Simulation of surface displacement produced by the Mw 8.1 mainshock, posted by Jean-Claude Ruegg.
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April 2, 10H (FR) posted by Anne Socquet:
GPS stations in northern Chile. cGPS in color circles, campaign as white triangles.
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April 2, 10h21 (FR) posted by Rémy Bossu: Figure by Stephen Hicks showing the previous seismicity.
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April 2, 10h50. Posted by Rémy Bossu: The seismic coupling in northern Chile as seen by Metois et al.
April 4. Posted by Sébastien Hok. Preliminary slip inversion for the first mainshock (Mw 8.1) by Gavin Hayes (USGS) using body and surface waves at teleismic distance (http://earthquake.usgs.gov/earthquakes/eventpage/usc000nzvd#scientific_finite-fault).
Commentaire de Sébastien Hok: Montre une aspérité principale au sud-est de l’épicentre, à proximité de la ville d’Iquique. Cette aspérité est localisée au même endroit que le maximum de couplage du modèle publié par Métois et al. 2013. La réplique du 3 avril se situe à la bordure sud de cette aspérité.
April 2, 21h53 (FR). Posted by Mohamed Chlieh. The seismic coupling in northern Chile as seen by M. Chlieh et al..
----------------------------------------------------------------- DETAILED TSUNAMI INFORMATION -----------------------------------------------
Details about the tsunami:
THE TSUNAMI WARNING AND/OR WATCH ISSUED BY THE PACIFIC TSUNAMI
WARNING CENTER IS NOW CANCELLED FOR
CHILE / PERU / ECUADOR / COLOMBIA / PANAMA / COSTA RICA /
NICARAGUA / EL SALVADOR / GUATEMALA / MEXICO / HONDURAS /
ANTARCTICA / PITCAIRN / FRENCH POLYNESIA
MEASUREMENTS OR REPORTS OF TSUNAMI WAVE ACTIVITY
GAUGE LOCATION LAT LON TIME AMPL PER
------------------- ----- ------ ----- --------------- -----
JUAN FERNANDEZ 33.6S 78.8W 0215Z 0.16M / 0.5FT 36MIN
SAN FELIX CL 26.3S 80.1W 0137Z 0.68M / 2.2FT 06MIN
COQUIMBO CL 30.0S 71.3W 0138Z 0.15M / 0.5FT 34MIN
CALDERA CL 27.1S 70.8W 0102Z 0.11M / 0.4FT 30MIN
CHANARAL CL 26.4S 70.6W 0133Z 0.24M / 0.8FT 28MIN
CALLAO LA-PUNTA PE 12.1S 77.2W 0158Z 0.12M / 0.4FT 38MIN
ARICA CL 18.5S 70.3W 0116Z 1.83M / 6.0FT 18MIN
MATARANI PE 17.0S 72.1W 0127Z 0.58M / 1.9FT 08MIN
PAPOSO CL 25.0S 70.5W 0125Z 0.26M / 0.9FT 22MIN
PISAGUA CL 19.6S 70.2W 0055Z 2.01M / 6.6FT 12MIN
MEJILLONES CL 23.1S 70.5W 0103Z 0.86M / 2.8FT 34MIN
TOCOPILLA CL 22.1S 70.2W 0109Z 0.42M / 1.4FT 10MIN
DART 32402 26.7S 74.0W 0044Z 0.05M / 0.2FT 44MIN
ANTOFAGASTA CL 23.7S 70.4W 0034Z 0.25M / 0.8FT 18MIN
PATACHE CL 20.8S 70.2W 0015Z 1.51M / 5.0FT 10MIN
IQUIQUE CL 20.2S 70.1W 0005Z 2.11M / 6.9FT 12MIN
LAT - LATITUDE (N-NORTH, S-SOUTH)
LON - LONGITUDE (E-EAST, W-WEST)
TIME - TIME OF THE MEASUREMENT (Z IS UTC IS GREENWICH TIME)
AMPL - TSUNAMI AMPLITUDE MEASURED RELATIVE TO NORMAL SEA LEVEL.
IT IS ...NOT... CREST-TO-TROUGH WAVE HEIGHT.
VALUES ARE GIVEN IN BOTH METERS(M) AND FEET(FT).
PER - PERIOD OF TIME IN MINUTES(MIN) FROM ONE WAVE TO THE NEXT.
NOTE - DART MEASUREMENTS ARE FROM THE DEEP OCEAN AND THEY
ARE GENERALLY MUCH SMALLER THAN WOULD BE COASTAL
MEASUREMENTS AT SIMILAR LOCATIONS.
EVALUATION
SEA LEVEL READINGS INDICATE A TSUNAMI WAS GENERATED. IT MAY HAVE
BEEN DESTRUCTIVE ALONG COASTS NEAR THE EARTHQUAKE EPICENTER. FOR
THOSE AREAS - WHEN NO MAJOR WAVES ARE OBSERVED FOR TWO HOURS
AFTER THE ESTIMATED TIME OF ARRIVAL OR DAMAGING WAVES HAVE NOT
OCCURRED FOR AT LEAST TWO HOURS THEN LOCAL AUTHORITIES CAN ASSUME
THE THREAT IS PASSED. DANGER TO BOATS AND COASTAL STRUCTURES CAN
CONTINUE FOR SEVERAL HOURS DUE TO RAPID CURRENTS. AS LOCAL
CONDITIONS CAN CAUSE A WIDE VARIATION IN TSUNAMI WAVE ACTION THE
ALL CLEAR DETERMINATION MUST BE MADE BY LOCAL AUTHORITIES.
NO TSUNAMI THREAT EXISTS FOR OTHER COASTAL AREAS ALTHOUGH SOME
MAY EXPERIENCE SMALL SEA LEVEL CHANGES. FOR ALL AREAS COVERED BY
THIS CENTER...THE TSUNAMI WARNING AND WATCH ARE CANCELLED.
================ Earthquake DATA second mainshock Mw 7.6 ===================
Localisation EMSC:
Magnitude Mw 7.6
Region OFFSHORE TARAPACA, CHILE
Date time 2014-04-03 02:43:17.0 UTC
Location 20.52 S ; 70.47 W
Depth 21 km
Localisation DGF Chile:
Hora UTC 02:43:15 03/04/2014
Latitud -20.517
Longitud -70.439
Profundidad 27.7 Km
Moment magnitude, focal mechanism, and depth from waveform inversions:
Comment: the expected rupture plane is the low angle east-dipping plane, with almost pure thrust faulting.
April 3, 9h44 (FR): Simulation of surface displacement produced by the second mainshock (Mw 7.6), posted by Jean-Claude Ruegg.
--> See pdf file at the end of the page
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