Marie-Paule Bouin

How fast is rupture during an earthquake? New insights from the 1999 Turkey Earthquakes

We report that during the two devastating 1999 earthquakes in Turkey, rupture propagated over a large part of the nearly 200km long fault zone at supershear speed approaching 5km/s. We present observations and modeling which confirm the original inference of supershear rupture during the Izmit earthquake and we show that supershear rupture also occurred during the Duzce earthquake. We show that the rupture velocity measured—about √2 times the shear wave velocity—is the value predicted by theoretical studies in fracture dynamics. We look for clues to explain these observations.

Extended Nucleation of the 1999 Mw 7.6 Izmit Earthquake

Low-frequency seismic events may have been part of slip accumulation before a large earthquake. Laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture. We report here that one of the best-recorded large earthquakes to date, the 1999 moment magnitude (Mw) 7.6 Izmit (Turkey) earthquake, was preceded by a seismic signal of long duration that originated from the hypocenter. The signal consisted of a succession of repetitive seismic bursts, accelerating with time, and increased low-frequency seismic noise. These observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust. This slip accelerated slowly initially, and then rapidly accelerated in the 2 minutes preceding the earthquake.

Space and Time Evolution of Rupture and Faulting during the 1999 İzmit (Turkey) Earthquake

We use the records of the ground motion obtained at near-fault accelerometers to study the space and time evolution of rupture and faulting during the Izmit earthquake. We find that the rupture propagated at the sub-Rayleigh speed of about 3 km/sec on the western and eastern segments of the fault, but that the central segment (Izmit-Sapanca Lake-Sakarya), nearly 50 km long, broke at the supershear speed of about 4.8 km/sec. This value, within the range of uncertainties, is the one theoretically predicted ( \(\sqrt{2}V_{\mathrm{S}}\) ) in fracture dynamics for stable shear crack growth at intersonic speed. We infer an average fault slip of about 2.9 m over a total rupture length of about 150 km, with the largest values (of up to 6 m) occurring in the Golcuk area to the west and in the Sakarya region to the east. The strong-motion data also indicate that the slip diminished gradually to the west beyond the Hersek peninsula over about 30 km, whereas it stopped abruptly at depth at the termination of the eastern (Karadere) segment. The slip duration is between 2 and 4 sec, except in the hypocentral area, which slipped in about 1 sec. The seismic moment inferred is about 2.5 × 10 20 N m.

Seismic imaging of the 1999 Izmit (Turkey) Rupture inferred from the near-fault recordings

We use near-fault accelerograms to infer the space-time history of rupture on the fault during the Izmit earthquake. The records show that the ground displacement and velocity near the fault were surprisingly simple. Rupture propagated toward the west at a velocity of about 3 km/s, and toward the east at a remarkably high average velocity of 4.7 km/s over a distance of about 45 km before decelerating to about 3.1 km/s on the eastern segment. Slip on the fault is particularly large down to a depth of 20 km on the central portion of the fault where it reaches about 7 m. Slip is large also below 10 km on the eastern fault segment, and this may have contributed to the loading of shear stress on the Duzce fault. On the western fault segment, large slip seems confined to shallow depths.

The Seismicity in the Eastern Marmara Sea after the 17 August 1999 İzmit Earthquake

We used seismic stations that we deployed after the Izmit earthquake along the shores and islands of the Izmit Bay-Cinarcik basin to study the seismic activity that took place after the earthquake in the eastern Marmara Sea. The aftershock distribution indicates the existence of three clusters of activity there in the days that followed the earthquake. One of the clusters shows the extension of the E-W-trending Izmit rupture into the eastern Marmara Sea. The seismic activity there clearly outlines the fault plane of the main rupture and shows its termination 35 km beyond the Hersek peninsula. Two other clusters of activity are present in the region. One is in the Armutlu peninsula and the other one is located a few kilometers southwest of the Tuzla peninsula beneath the northern slope of the Cinarcik basin. The focal mechanism solutions indicate strike-slip faulting along the main branch of the Izmit rupture and normal faulting within the two swarms. The presence of the different mechanisms suggests the existence of slip partitioning in the region. A remarkable feature of the aftershock data is the absence of seismicity above 4 km in the Marmara Sea. Manuscript received 30 August 2000.

The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic observations

After the January 12, 2010, Haiti earthquake, we deployed a mainly offshore temporary network of seismologic stations around the damaged area. The distribution of the recorded aftershocks, together with morphotectonic observations and mainshock analysis, allow us to constrain a complex fault pattern in the area. Almost all of the aftershocks have a N‐S compressive mechanism, and not the expected left‐lateral strike‐slip mechanism. A first‐order slip model of the mainshock shows a N264°E north‐dipping plane, with a major left‐lateral component and a strong reverse component. As the aftershock distribution is sub‐parallel and close to the Enriquillo fault, we assume that although the cause of the catastrophe was not a rupture along the Enriquillo fault, this fault had an important role as a mechanical boundary. The azimuth of the focal planes of the aftershocks are parallel to the north‐dipping faults of the Transhaitian Belt, which suggests a triggering of failure on these discontinuities. In the western part, the aftershock distribution reflects the triggering of slip on similar faults, and/or, alternatively, of the south‐dipping faults, such the Trois‐Baies submarine fault. These observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the Southern Peninsula and the sedimentary wedge of the Transhaitian Belt: the rupture occurred on a wrench fault at the rheologic boundary on top of the under‐thrusting rigid oceanic block, whereas the aftershocks were the result of the relaxation on the hanging wall along pre‐existing discontinuities in the frontal part of the Transhaitian Belt.

Tarapacá intermediate‐depth earthquake (Mw 7.7, 2005, northern Chile): A slab‐pull event with horizontal fault plane constrained from seismologic and geodetic observations

[1] A large (Mw 7.7) intermediate-depth earthquake occurred on 13 June 2005 in the Tarapaca region of the northern Chile seismic gap. Source parameters are inferred from teleseismic broadbands, strong motions, GPS and InSAR data. Relocated hypocenter is found at

Crustal Structure and Fault Geometry of the 2010 Haiti Earthquake from Temporary Seismometer Deployments

98 km depth within the subducting slab. The 21-days aftershock distribution, constrained by a postseismic temporary array, indicates a sub-horizontal fault plane lying between the planes of the double seismic zone and an upper bound of the rupture area of 60 km  30 km. Teleseismic inversion shows a slab-pull down dip extension mechanism on a nearly horizontal plane. Total seismic and geodetic moments are

Multiscale Mapping of Completeness Magnitude of Earthquake Catalogs

5.5 Â 10 20 N.m, with an averaged slip of 6.5 m from geodesy. The earthquake rupture is peculiar in that the effective velocity is slow, 3.5 Km.s A1 for a high stress-drop, 21 –30 MPa. We propose that rupture was due to the reactivation by hydraulic embrittlement of a inherited major lithospheric fault within the subducting plate. The stress-drop suggests that the region of the slab between planes of the double seismic zone can sustain high stresses. Citation: Peyrat, S., et al. (2006), Tarapaca intermediate-depth earthquake (Mw 7.7, 2005, northern Chile): A slab-pull event with horizontal fault plane constrained from seismologic and geodetic observations, Geophys.

Seismic and electrical anisotropy in the Mornos Delta, Gulf of Corinth, Greece, and its relationship with GPS strain measurements

Haiti has been the locus of a number of large and damaging historical earthquakes. The recent 12 January 2010 Mw 7.0 earthquake affected cities that were largely unprepared, which resulted in tremendous losses. It was initially assumed that the earthquake ruptured the Enriquillo Plantain Garden fault (EPGF), a major active structure in southern Haiti, known from geodetic measurements and its geomorphic expression to be capable of producing M 7 or larger earthquakes. Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data, however, showed that the event ruptured a previously unmapped fault, the Leogâne fault, a north‐dipping oblique transpressional fault located immediately north of the EPGF. Following the earthquake, several groups installed temporary seismic stations to record aftershocks, including ocean‐bottom seismometers on either side of the EPGF. We use data from the complete set of stations deployed after the event, on land and offshore, to relocate all aftershocks from 10 February to 24 June 2010, determine a 1D regional crustal velocity model, and calculate focal mechanisms. The aftershock locations from the combined dataset clearly delineate the Leogâne fault, with a geometry close to that inferred from geodetic data. Its strike and dip closely agree with the global centroid moment tensor solution of the mainshock but with a steeper dip than inferred from previous finite fault inversions. The aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone, which could indicate triggered seismicity on the offshore Trois Baies reverse fault. We use first‐motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.