Seismic analysis for the Lanzhou fireball

In this paper, we convert the Lanzhou fireball's trajectory using seismic data according to the analytical method presented in Pujol et al. (2005, 2006). Taking the same assumptions as Pujol et al., the position of the fireball burst at its terminal has been converted using a relative simple independent method. Both the trajectory and the position of burst are roughly coincident.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Growing correlation length of moderate-sized earthquakes prior to two great earthquakes near Sumatra Island

Seismic correlation length for moderate earthquakes prior to two great earthquakes in the northern sea area of Sumatra Island (Mw9.1 in 2004 and Ms8. 6 in 2012) has been studied, using method of Single-Link-Cluster (SLC) analysis, and found to show a power-law growth about two years before their occurrences. No such growth was found for a magnitude 7 earthquake in the same area. This result suggests the occurrence of a physical process of critical-point characteristics in the source area before the great earthquakes

Source parameters and tectonic origin of the 1996 June 1 Tianzhu (M<SUB>w</SUB>=5.2) and 1995 July 21 Yongden (M<SUB>w</SUB>=5.6) earthquakes near the Haiyuan fault (Gansu, China)

International audienceThe 1996 June 1 Tianzhu (Mw=5.2, Ms=4.9) and the 1995 July 21 Yongden (Mw=5.6, Ms=5.4) earthquakes are the two largest events recorded in the last 10 years between the 1990 October 20 Ms=5.8 and the recent 2000 June 6 Ms=5.6 earthquakes near the `Tianzhu seismic gap' on the Haiyuan fault in northeastern Tibet. We use frequency-time analysis (FTAN) to extract the fundamental modes of Love and Rayleigh waves from digital records. A joint inversion of their amplitude spectra and of P-wave first-motion polarities is then performed to calculate the source parameters (focal mechanisms, depths and seismic moments) of these two Ms~=5 earthquakes. Such a joint inversion is tested for the first time. We use IRIS and GEOSCOPE network records for period ranges of 20-40s for the former event and 35-70s for the latter. The inversion of the Tianzhu earthquake yields nodal planes with strike, dip and slip of 282°, 72° and 3° and 191°, 87° and 162°, respectively, a focal depth around 12km and a seismic moment of 0.56×1017Nm, consistent with the Harvard CMT calculation, and the alignment and depths of the aftershocks recorded by a local network. We propose two possible tectonic interpretations for this off-fault event. The solution for the Yongden earthquake is consistent with a thrust, with strike, dip and slip of 105°, 45° and 75°, respectively, a focal depth around 6km and a seismic moment of 2.4×1017Nm, also in agreement with the Harvard CMT mechanism, the distribution of the aftershocks recorded by a regional network, and the general tectonic setting that we refine

Spatio-temporal evolution of aseismic slip along the Haiyuan fault, China: Implications for fault frictional properties

International audienceWe use 20 years of Synthetic Aperture Radar acquisitions by the ERS and Envisat satellites to investigate the spatial and temporal variations of strain rates along the 35-km long creeping section of the Haiyuan fault, at the north eastern boundary of the Tibetan plateau. We then use the derived displacements to infer the faultʼs frictional properties and discuss the relationship between creep and the seismic behavior of the fault. Located in between a millennial seismic gap and the 1920 M8 surface rupture trace, this section has an average creep rate of image, about the interseismic loading rate. The comparison of average surface velocity profiles derived from SAR interferometry across the creeping section reveals a creep rate increase and/or a creep migration to shallower depth between the 1990s and the 2000s. We apply a smoothed time series analysis scheme on Envisat InSAR data to investigate the creep rate variations during the 2004-2009 time period. Our analysis reveals that the creep rate accelerated in 2007, although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude. Both decadal and short term transient behaviors are coeval with the largest earthquakes image along the fault segment in recent years. From the precise mapping of the surface fault trace, we use the fault strike variations and the Mohr circle construction to compute the along-strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate. We find that the creep rate scales logarithmically with the friction coefficient, in agreement with the rate-and-state friction law in a rate strengthening regime. The estimated value of image indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segmentʼs creep rate and that the recorded micro seismicity is most likely creep-driven. Finally, given the size and frictional properties of the creeping section, we estimate, based on previous models of dynamic rupture simulations, a 0-20% probability for a rupture to break through this section. Together with the geometrical configuration of the Haiyuan fault, these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation