scholarly journals Solving the Puzzle of the September 2018 Palu, Indonesia, Tsunami Mystery: Clues from the Tsunami Waveform and the Initial Field Survey Data

2018 ◽  
Vol 13 (Scientific Communication) ◽  
pp. sc20181108 ◽  
Author(s):  
Abdul Muhari ◽  
Fumihiko Imamura ◽  
Taro Arikawa ◽  
Aradea R. Hakim ◽  
Bagus Afriyanto ◽  
...  
Keyword(s):  
Preliminary Analysis ◽  
Field Survey ◽  
Strike Slip ◽  
Flow Depth ◽  
Initial Field ◽  
Bathymetric Data ◽  
Underwater Landslide ◽  
Short Period ◽  
Extensive Property ◽  
Tsunami Waveform

On September 28, 2018, following a magnitude 7.5 strike-slip fault earthquake, an unexpected tsunami inundated the coast of Palu bay, Sulawesi, Indonesia, causing many casualties and extensive property damage. However, the earthquake’s mechanism rarely generates a destructive tsunami. The tidal record at Pantoloan, located along the coast of Palu bay, indicates that the tsunami arrived 6 min after the earthquake and generated 2 m of receding water. It had a maximum wave height of 2 m and arrived approximately 2 min later. The tsunami had a relatively short period and caused devastation as far inland as 300 m. Additionally, 8 m high watermarks were observed near the coast; the flow depth decreased to 3.5 m inland (Fig. 1). Amateur videos and eyewitness accounts indicate that the tsunami did not enter the bay through its mouth but obliquely from an area inside the bay. Our hypothesis, therefore, is that the killer tsunami was most likely generated by an underwater landslide occurring inside Palu bay. While detailed bathymetric data are still needed to confirm this hypothesis, in this article we provide a preliminary analysis of the available data, supported by the results of a field survey, to strengthen this hypothesis and provide direction for further post-tsunami surveys and analysis.

Aftershocks and surface faulting associated with the intraplate Guinea, West Africa, earthquake of 22 December 1983

1987 ◽  
Vol 77 (5) ◽  
pp. 1579-1601
Author(s):  
C. J. Langer ◽  
M. G. Bonilla ◽  
G. A. Bollinger
Keyword(s):  
West Africa ◽  
Focal Mechanism ◽  
Main Shock ◽  
Strike Slip ◽  
Fault System ◽  
Epicentral Area ◽  
Lateral Strike Slip ◽  
Focal Mechanism Solutions ◽  
Short Period ◽  
East West

Abstract This study reports on the results of geological and seismological field studies conducted following the rare occurrence of a moderate-sized West African earthquake (mb = 6.4) with associated ground breakage. The epicentral area of the northwestern Guinea earthquake of 22 December 1983 is a coastal margin, intraplate locale with a very low level of historical seismicity. The principal results include the observation that seismic faulting occurred on a preexisting fault system and that there is good agreement among the surface faulting, the spatial distribution of the aftershock hypocenters, and the composite focal mechanism solutions. We are not able, however, to shed any light on the reason(s) for the unexpected occurrence of this intraplate earthquake. Thus, the significance of this study is its contribution to the observational datum for such earthquakes and for the seismicity of West Africa. The main shock was associated with at least 9 km of surface fault-rupture. Trending east-southeast to east-west, measured fault displacements up to ∼13 cm were predominantly right-lateral strike slip and were accompanied by an additional component (5 to 7 cm) of vertical movement, southwest side down. The surface faulting occurred on a preexisting fault whose field characteristics suggest a low slip rate with very infrequent earthquakes. There were extensive rockfalls and minor liquefaction effects at distances less than 10 km from the surface faulting and main shock epicenter. Main shock focal mechanism solutions derived from teleseismic data by other workers show a strong component of normal faulting motion that was not observed in the ground ruptures. A 15-day period of aftershock monitoring, commencing 22 days after the main shock, was conducted. Eleven portable, analog short-period vertical seismographs were deployed in a network with an aperture of 25 km and an average station spacing of 7 km. Ninety-five aftershocks were located from the more than 200 recorded events with duration magnitudes of about 1.5 or greater. Analysis of a selected subset (91) of those events define a tabular aftershock volume (26 km long by 14 km wide by 4 km thick) trending east-southeast and dipping steeply (∼60°) to the south-southwest. Composite focal mechanisms for groups of events, distributed throughout the aftershock volume, exhibit right-lateral, strike-slip motion on subvertical planes that strike almost due east. Although the general agreement between the field geologic and seismologic results is good, our preferred interpretation is for three en-echelon faults striking almost due east-west.

Short Period Oscillations in Acturus, Aldebaran, and Pollux

1988 ◽  
Vol 132 ◽  
pp. 291-294
Author(s):  
Peter H. Smith ◽  
Robert S. McMillan
Keyword(s):  
Time Series ◽  
Preliminary Analysis ◽  
Time Series Data ◽  
Careful Analysis ◽  
Series Data ◽  
Short Period ◽  
Stellar Velocity ◽  
Clean Algorithm ◽  
K Giants

A total of 48 nights of time series data have been obtained for the K giants: Arcturus, Pollux, and Aldebaran. A careful analysis of both single and multi–night sets using the earth's motion as a velocity calibrator has yielded stellar velocity time series accurate to ± 3 m/s per observation. Periodogram analyses of these sets have revealed the existence of oscillations with periods near 2.5 hrs and amplitudes of ± 5 m/s for both Pollux and Aldebaran, but not for Arcturus. Preliminary analysis of a 5-night set for Pollux using the CLEAN algorithm suggests at least three modes separated by about 35 microHertz.

scholarly journals HST Observations of 3 More Old LMC Clusters

2002 ◽  
Vol 207 ◽  
pp. 190-192
Author(s):  
Jennifer A. Johnson ◽  
Michael Bolte ◽  
Peter B. Stetson ◽  
James E. Hesser
Keyword(s):  
Age Differences ◽  
Large Volume ◽  
Preliminary Analysis ◽  
Cluster Formation ◽  
Star Cluster ◽  
Initial Epoch ◽  
Short Period

We present color-magnitude diagrams (CMDs) based on HST F555W (“V”) and F814W (“I”) observations of three old LMC clusters: NGC 2210, NGC 1786, and Reticulum. The fiducial derived from the CMD of NGC 2257, another LMC cluster, provided a good fit to the data for the new clusters. Because NGC 2257 has a similar metallicity ([Fe/H]∼ −1.8) to NGC 2210, NGC 1786, and Reticulum, the agreement between the CMDs of all four clusters indicates that they have the same age. This preliminary analysis suggests that any age differences are smaller than 2 Gyr. These new results mean that there are now 11 old LMC clusters with similar ages. An initial epoch of star cluster formation therefore happened in a short period over a large volume of space, a volume much larger than is now covered by the present-day optical LMC.

Study of the tsunami source in the Palu Bay following the Mw7.5 2018 Sulawesi earthquake

2020 ◽  
Author(s):  
Fabrizio Romano ◽  
Haider Hasan ◽  
Stefano Lorito ◽  
Finn Løvholt ◽  
Beatriz Brizuela ◽  
...  
Keyword(s):  
Tide Gauge ◽  
Joint Inversion ◽  
Seismic Source ◽  
Strike Slip ◽  
Tsunami Source ◽  
Fault System ◽  
Tsunami Propagation ◽  
Slip Mechanism ◽  
Short Period ◽  
Nonlinear Joint

<p>On 28 September 2018 a Mw 7.5 strike-slip earthquake occurred on the Palu-Koro fault system in the Sulawesi Island. Immediately after the earthquake a powerful tsunami hit the Palu Bay causing large damages and numerous fatalities.</p><p>Several works, inverting seismic or geodetic data, clearly estimated the slip distribution of this event, but the causative source of the tsunami is still not completely understood; indeed, the strike-slip mechanism of the seismic source alone might not be sufficient to explain the large runups observed (> 6 m) along the coast of the Palu Bay, and thus one or more additional non-seismic sources like a landslide could have contributed to generate the big tsunami. An insight of that can be found in an extraordinary collection of amateur videos, and on the only available tide gauge in the Bay, at Pantoloan, that showed evidence for a short period wave of at least 2-3 minutes, compatible with a landslide.</p><p>In this study, we attempt to discriminate the contribution in the tsunami generation of both the seismic source and  some supposed landslides distributed along the coast of the Bay.</p><p>In particular, we attempt to estimate the causative source of the tsunami by means of a nonlinear joint inversion of geodetic (InSAR) and runup data. We use a fault geometry consistent with the Sentinel-2 optical analysis results and analytically compute the geodetic Green’s functions. The same fault model is used to compute the initial condition for the seismic tsunami Green’s functions, including the contribution of the horizontal deformation due to the gradient of the bathymetry (10 m spatial resolution); the landslide tsunami Green’s functions are computed the software BingClaw by placing several hypothetical sources in the Bay. In both the cases the tsunami propagation is modelled by numerically solving the nonlinear shallow water equations.</p><p>In this work we also attempt to address the validity of Green’s functions approach (linearity) for earthquake and landslide sources as well as the wave amplitude offshore as predictor of nearby runup.</p>

Field Survey of Mw8.8 Feb. 27, 2010 Chile Earthquake and Tsunami

2011 ◽  
Vol 250-253 ◽  
pp. 2102-2106 ◽  
Author(s):  
Rui Zhi Wen ◽  
Bai Tao Sun ◽  
Bao Feng Zhou
Keyword(s):  
Preliminary Analysis ◽  
Field Survey ◽  
Strong Motion ◽  
Building Damage ◽  
Great Earthquake ◽  
Chinese Scientist ◽  
Yushu Earthquake ◽  
Motion Data ◽  
Chile Earthquake ◽  
China Earthquake

In this paper, it is a brief summary for the field survey on the 27 February, 2010 Malue mega-earthquake, Chile by a Chinese scientist team. This mission is to investigate the reason why such a great earthquake caused less causalities, less loss compared with Chinese Wenchuan and Yushu earthquake. This survey was sponsored by China Earthquake Administration and this paper focused on the strong motion data analysis, some building damage observation and tsunami. We gave a preliminary analysis for the strong motions characteristic and some typical building damage. The understanding of this great earthquake could be improved our knowledge for advancing societal resilience.

The 2018 Palu Tsunami: Coeval Landslide and Coseismic Sources

2020 ◽  
Vol 91 (6) ◽  
pp. 3148-3160
Author(s):  
Amy L. Williamson ◽  
Diego Melgar ◽  
Xiaohua Xu ◽  
Christopher Milliner
Keyword(s):  
Survey Data ◽  
Field Survey ◽  
Tide Gauge ◽  
Hazard Analysis ◽  
Strike Slip ◽  
Coseismic Deformation ◽  
Coseismic Slip ◽  
Video Footage ◽  
Run Up ◽  
Tsunami Model

Abstract On 28 September 2018, Indonesia was struck by an MW 7.5 strike-slip earthquake. An unexpected tsunami followed, inundating nearby coastlines leading to extensive damage. Given the traditionally non-tsunamigenic mechanism, it is important to ascertain if the source of the tsunami is indeed from coseismic deformation, or something else, such as shaking induced landsliding. Here we determine the leading cause of the tsunami is a complex combination of both. We constrain the coseismic slip from the earthquake using static offsets from geodetic observations and validate the resultant “coseismic-only” tsunami to observations from tide gauge and survey data. This model alone, although fitting some localized run-up measurements, overall fails to reproduce both the timing and scale of the tsunami. We also model coastal collapses identified through rapidly acquired satellite imagery and video footage as well as explore the possibility of submarine landsliding using tsunami raytracing. The tsunami model results from the landslide sources, in conjunction with the coseismic-generated tsunami, show a greatly improved fit to both tide gauge and field survey data. Our results highlight a case of a damaging tsunami the source of which is a complex mix of coseismic deformation and landsliding. Tsunamis of this nature are difficult to provide warning for and are underrepresented in regional tsunami hazard analysis.

Inversion of regional surface-wave spectra for source parameters of aftershocks from the Loma Prieta earthquake

1991 ◽  
Vol 81 (5) ◽  
pp. 1726-1736
Author(s):  
Susan L. Beck ◽  
Howard J. Patton
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
P Wave ◽  
Wave Spectra ◽  
Short Period ◽  
First Motion

Abstract Surface waves recorded at regional distances are used to study the source parameters for three of the larger aftershocks of the 18 October 1989, Loma Prieta, California, earthquake. The short-period P-wave first-motion focal mechanisms indicate a complex aftershock sequence with a wide variety of mechanisms. Many of these events are too small for teleseismic body-wave analysis; therefore, the regional surface-waves provide important long-period information on the source parameters. Intermediate-period Rayleigh- and Love-wave spectra are inverted for the seismic moment tensor elements at a fixed depth and repeated for different depths to find the source depth that gives the best fit to the observed spectra. For the aftershock on 19 October at 10:14:35 (md = 4.2), we find a strike-slip focal mechanism with right lateral motion on a NW-trending vertical fault consistent with the mapped trace of the local faults. For the aftershock on 18 October at 10:22:04 (md = 4.4), the surface waves indicate a pure reverse fault with the nodal planes striking WNW. For the aftershock on 19 October at 09:53:50 (md = 4.4), the surface waves indicate a strike-slip focal mechanism with a NW-trending vertical nodal plane consistent with the local strike of the San Andreas fault. Differences between the surface-wave focal mechanisms and the short-period P-wave first-motion mechanisms are observed for the aftershocks analyzed. This discrepancy may reflect the real variations due to differences in the band width of the two observations. However, the differences may also be due to (1) errors in the first-motion mechanism due to incorrect near-source velocity structure and (2) errors in the surface-wave mechanisms due to inadequate propagation path corrections.

Source Parameters of Large Australian Intracontinental Earthquakes

1988 ◽  
Vol 59 (4) ◽  
pp. 315-315
Author(s):  
Robert McCaffrey ◽  
Joanne Fredrich
Keyword(s):  
Continental Margin ◽  
Source Parameters ◽  
Strike Slip ◽  
Thrust Faulting ◽  
Long Period ◽  
The Past ◽  
Preliminary Examination ◽  
Short Period ◽  
Australian Continent ◽  
Large Earthquakes

Abstract We have examined the largest earthquakes in the Australian continent over the past 20 years by modeling their teleseismic long-period P and SH and short-period P waveforms. Eight earthquakes beneath the continent show thrust faulting at depths shallower than 10 km. Three (1, 2, 4 below) produced surface faulting and their waveforms indicate centroid depths of 3 km or less. The P-axes in the southwestern half of the continent have easterly trends. Preliminary examination of the 3 large earthquakes near Tennant Creek on 22 January, 1988, (7–9) indicate thrusting at less than 10 km depth, but with N-trending P-axes. The largest event (9), at 12:06 GMT, had a seismic moment of roughly 1019 Nm, which makes it comparable in size to the 1968 Meckering event (1). One event (6) beneath the continental margin indicates strike-slip at 26 km depth.

scholarly journals A new B-subdwarf eclipsing binary with an extremely short period

1986 ◽  
Vol 118 ◽  
pp. 305-306 ◽  
Author(s):  
J W Menzies ◽  
F Marang
Keyword(s):  
Light Curve ◽  
Preliminary Analysis ◽  
Eclipsing Binary ◽  
Common Envelope ◽  
Short Period

The B-type Subdwarf BD-07°3477 has been found to be an eclipsing binary with a period of about 2h48m. A preliminary analysis of the light curve reveals the system to be fully detached. It appears to be similar in many respects to the O-Subdwarf binary AA Dor which is thought to be the remnant of a system which has undergone a common envelope phase of evolution.

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