Managing injection-induced seismic risks Lee, Kang-Kun; Ellsworth, William L; Giardini, Domenico ...
Science (American Association for the Advancement of Science),
05/2019, Letnik:
364, Številka:
6442
Journal Article
Recenzirano
The Pohang quake shows the need for new methods to assess and manage evolving risk
Heat transported from deep within Earth's crust can be used to generate electricity or provide direct heating by ...circulating fluid through permeable fracture networks in hot rock. Because naturally permeable systems are rare, enhanced geothermal system (EGS) technology stimulates the creation of permeable pathways in otherwise impermeable rock by means of the injection of water under high pressure, creating new fractures and causing preexisting fractures to open. But several EGS projects have encountered problems of induced seismicity, particularly the moment magnitude (
M
w
) 5.5 earthquake in 2017 that occurred near an EGS drill site in Pohang, Republic of Korea (South Korea). Here we explore the implications of, and derive lessons from, the Pohang experience. The Pohang earthquake provides unequivocal evidence that EGS stimulation can trigger large earthquakes that rupture beyond the stimulated volume and disproves the hypothesis that the maximum earthquake magnitude is governed by the volume of injected fluids. Because that hypothesis tacitly underpins hazard-based methods used for managing induced seismicity, those methods must be revised and based on considerations of risk.
Seismic detection of the martian core Stähler, Simon C.; Khan, Amir; Banerdt, W. Bruce ...
Science (American Association for the Advancement of Science),
07/2021, Letnik:
373, Številka:
6553
Journal Article
Recenzirano
Odprti dostop
Single seismometer structure
Because of the lack of direct seismic observations, the interior structure of Mars has been a mystery. Khan
et al.
, Knapmeyer-Endrun
et al.
, and Stähler
et al.
used ...recently detected marsquakes from the seismometer deployed during the InSight mission to map the interior of Mars (see the Perspective by Cottaar and Koelemeijer). Mars likely has a 24- to 72-kilometer-thick crust with a very deep lithosphere close to 500 kilometers. Similar to the Earth, a low-velocity layer probably exists beneath the lithosphere. The crust of Mars is likely highly enriched in radioactive elements that help to heat this layer at the expense of the interior. The core of Mars is liquid and large, ∼1830 kilometers, which means that the mantle has only one rocky layer rather than two like the Earth has. These results provide a preliminary structure of Mars that helps to constrain the different theories explaining the chemistry and internal dynamics of the planet.
Science
, abf2966, abf8966, abi7730, this issue p.
434
, p.
438
, p.
443
see also abj8914, p.
388
Data from the InSight mission on Mars help constrain the structure and properties of the martian interior.
Clues to a planet’s geologic history are contained in its interior structure, particularly its core. We detected reflections of seismic waves from the core-mantle boundary of Mars using InSight seismic data and inverted these together with geodetic data to constrain the radius of the liquid metal core to 1830 ± 40 kilometers. The large core implies a martian mantle mineralogically similar to the terrestrial upper mantle and transition zone but differing from Earth by not having a bridgmanite-dominated lower mantle. We inferred a mean core density of 5.7 to 6.3 grams per cubic centimeter, which requires a substantial complement of light elements dissolved in the iron-nickel core. The seismic core shadow as seen from InSight’s location covers half the surface of Mars, including the majority of potentially active regions—e.g., Tharsis—possibly limiting the number of detectable marsquakes.
Single seismometer structure
Because of the lack of direct seismic observations, the interior structure of Mars has been a mystery. Khan
et al.
, Knapmeyer-Endrun
et al.
, and Stähler
et al.
used ...recently detected marsquakes from the seismometer deployed during the InSight mission to map the interior of Mars (see the Perspective by Cottaar and Koelemeijer). Mars likely has a 24- to 72-kilometer-thick crust with a very deep lithosphere close to 500 kilometers. Similar to the Earth, a low-velocity layer probably exists beneath the lithosphere. The crust of Mars is likely highly enriched in radioactive elements that help to heat this layer at the expense of the interior. The core of Mars is liquid and large, ∼1830 kilometers, which means that the mantle has only one rocky layer rather than two like the Earth has. These results provide a preliminary structure of Mars that helps to constrain the different theories explaining the chemistry and internal dynamics of the planet.
Science
, abf2966, abf8966, abi7730, this issue p.
434
, p.
438
, p.
443
see also abj8914, p.
388
Data from the InSight mission on Mars help constrain the structure and properties of the martian mantle.
A planet’s crust bears witness to the history of planetary formation and evolution, but for Mars, no absolute measurement of crustal thickness has been available. Here, we determine the structure of the crust beneath the InSight landing site on Mars using both marsquake recordings and the ambient wavefield. By analyzing seismic phases that are reflected and converted at subsurface interfaces, we find that the observations are consistent with models with at least two and possibly three interfaces. If the second interface is the boundary of the crust, the thickness is 20 ± 5 kilometers, whereas if the third interface is the boundary, the thickness is 39 ± 8 kilometers. Global maps of gravity and topography allow extrapolation of this point measurement to the whole planet, showing that the average thickness of the martian crust lies between 24 and 72 kilometers. Independent bulk composition and geodynamic constraints show that the thicker model is consistent with the abundances of crustal heat-producing elements observed for the shallow surface, whereas the thinner model requires greater concentration at depth.
Single seismometer structure
Because of the lack of direct seismic observations, the interior structure of Mars has been a mystery. Khan
et al.
, Knapmeyer-Endrun
et al.
, and Stähler
et al.
used ...recently detected marsquakes from the seismometer deployed during the InSight mission to map the interior of Mars (see the Perspective by Cottaar and Koelemeijer). Mars likely has a 24- to 72-kilometer-thick crust with a very deep lithosphere close to 500 kilometers. Similar to the Earth, a low-velocity layer probably exists beneath the lithosphere. The crust of Mars is likely highly enriched in radioactive elements that help to heat this layer at the expense of the interior. The core of Mars is liquid and large, ∼1830 kilometers, which means that the mantle has only one rocky layer rather than two like the Earth has. These results provide a preliminary structure of Mars that helps to constrain the different theories explaining the chemistry and internal dynamics of the planet.
Science
, abf2966, abf8966, abi7730, this issue p.
434
, p.
438
, p.
443
see also abj8914, p.
388
Data from the InSight mission on Mars help constrain the structure and properties of the martian interior.
For 2 years, the InSight lander has been recording seismic data on Mars that are vital to constrain the structure and thermochemical state of the planet. We used observations of direct (
P
and
S
) and surface-reflected (
PP
,
PPP
,
SS
, and
SSS
) body-wave phases from eight low-frequency marsquakes to constrain the interior structure to a depth of 800 kilometers. We found a structure compatible with a low-velocity zone associated with a thermal lithosphere much thicker than on Earth that is possibly related to a weak
S
-wave shadow zone at teleseismic distances. By combining the seismic constraints with geodynamic models, we predict that, relative to the primitive mantle, the crust is more enriched in heat-producing elements by a factor of 13 to 20. This enrichment is greater than suggested by gamma-ray surface mapping and has a moderate-to-elevated surface heat flow.
SUMMARY
Modelling the attenuation of shear wave energy is an important component of seismic hazard analysis. Previous studies have shown how attenuation, particularly in the uppermost layers of the ...crust, is regionally dependent. The impact of this is that the decay of energy radiating from an earthquake will vary from place to place. To quantify the regional attenuation in Switzerland we model the Fourier spectral amplitude of small‐to‐moderate earthquakes, recorded on the local seismic networks. High‐frequency decay is parametrized by Q and κ, while apparent geometrical spreading models account for the frequency‐independent decay of energy. We analyse ground motion encompassing the significant duration of shaking to provide models that are useful for the purpose of seismic hazard analysis. Two methods are used to estimate the whole path attenuation parameter, t*: first, a simultaneous fit of the source model and attenuation effects across the entire spectral bandwidth for earthquakes with M > 2; and secondly, a linear fit of an attenuation model to the high‐frequency part of the spectrum for earthquakes with M > 3.5. The t* parameter is found to vary with hypocentral distance consistent with a weakly attenuating crust and strongly attenuating uppermost layer. 1‐D tomographic inversions indicate a profile of increasing Q with depth down to the Moho. Frequency‐independent decay is parametrized using a three‐part model which allows for the inclusion of Moho reflection phases in the spectrum in the range of 20–140 km in the Swiss Foreland and from 70 to 140 km in the Swiss Alps.
S1222a—The Largest Marsquake Detected by InSight Kawamura, Taichi; Clinton, John F.; Zenhäusern, Géraldine ...
Geophysical research letters,
16 March 2023, Letnik:
50, Številka:
5
Journal Article
Recenzirano
Odprti dostop
NASA's InSight has detected a large magnitude seismic event, labeled S1222a. The event has a moment magnitude of MWMa ${\mathrm{M}}_{\mathrm{W}}^{\text{Ma}}$4.7, with five times more seismic moment ...compared to the second largest event. The event is so large that features are clearly observed that were not seen in any previously detected events. In addition to body phases and Rayleigh waves, we also see Love waves, minor arc surface wave overtones, and multi‐orbit surface waves. At long periods, the coda event exceeds 10 hr. The event locates close to the North‐South dichotomy and outside the tectonically active Cerberus Fossae region. S1222a does not show any evident geological or tectonic features. The event is extremely rich in frequency content, extending from below 1/30 Hz up to 35 Hz. The event was classified as a broadband type event; we also observe coda decay and polarization similar to that of very high frequency type events.
Plain Language Summary
After 3 years of seismic monitoring of Mars by InSight Seismic Experiment for Interior Structure instrument, we detected a marsquake largest ever observed during the mission. The event is larger by factor of 5 in seismic moment compared to previously detected events. With such an energetic event, we discovered various seismic features that was never observed before. For the first time, we were able to detect body waves and surface waves with their overtones. The large variety of detected seismic phases will enable us to probe the internal structure of Mars. Second, the event was located outside a well‐known seismically active region of Cerberus Fossae. This might indicate that event do not come from the same fault system with other major marsquakes. Finally, this event shows simultaneously features of marsquakes that were previously classified into different types. S1222a is classified as a broadband event with a wide frequency range of seismic energy. At the same time, the coda shape and decay at high frequency resembles that of very high frequency type events. It was an open question how different types of marsquakes are excited of what makes such differences and such event will be a key to uncover such mystery of marsquakes.
Key Points
InSight detected on 4 May 2022 a MWMa ${\mathrm{M}}_{\mathrm{W}}^{\text{Ma}}$4.7 marsquake, S1222a, which is the largest seismic event detected so far
The exceptional signal‐to‐noise allows multiple phases to be identified, with a rich collection of surface waves
S1222a was located 37° southeast of the InSight landing site and close to the Martian dichotomy boundary
We have developed a network optimization method for regional-scale microseismic monitoring networks and applied it to optimize the densification of the existing seismic network in northeastern ...Switzerland. The new network will build the backbone of a 10-yr study on the neotectonic activity of this area that will help to better constrain the seismic hazard imposed on nuclear power plants and waste repository sites. This task defined the requirements regarding location precision (0.5 km in epicentre and 2 km in source depth) and detection capability magnitude of completeness M
c = 1.0 (M
L). The goal of the optimization was to find the geometry and size of the network that met these requirements. Existing stations in Switzerland, Germany and Austria were considered in the optimization procedure.
We based the optimization on the simulated annealing approach proposed by Hardt & Scherbaum, which aims to minimize the volume of the error ellipsoid of the linearized earthquake location problem (D-criterion). We have extended their algorithm to:
calculate traveltimes of seismic body waves using a finite difference ray tracer and the 3-D velocity model of Switzerland,
calculate seismic body-wave amplitudes at arbitrary stations assuming the Brune source model and using scaling and attenuation relations recently derived for Switzerland, and
estimate the noise level at arbitrary locations within Switzerland using a first-order ambient seismic noise model based on 14 land-use classes defined by the EU-project CORINE and open GIS data.
We calculated optimized geometries for networks with 10-35 added stations and tested the stability of the optimization result by repeated runs with changing initial conditions. Further, we estimated the attainable magnitude of completeness (M
c) for the different sized optimal networks using the Bayesian Magnitude of Completeness (BMC) method introduced by Mignan et al.
The algorithm developed in this study is also applicable to smaller optimization problems, for example, small local monitoring networks. Possible applications are volcano monitoring, the surveillance of induced seismicity associated with geotechnical operations and many more. Our algorithm is especially useful to optimize networks in populated areas with heterogeneous noise conditions and if complex velocity structures or existing stations have to be considered.
Because of the strongly increased seismic activity felt at the surface, injection was stopped on 7 December. Dams can break, nuclear power plants may fail, carbon dioxide released from the oil and ...gas contributes to global warming, and EGS projects can create damage through induced earthquakes.
Pre-mission InSights on the Interior of Mars Smrekar, Suzanne E.; Lognonné, Philippe; Spohn, Tilman ...
Space science reviews,
02/2019, Letnik:
215, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Interior exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) Mission will focus on Mars’ interior structure and evolution. The basic structure of crust, mantle, and ...core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our understanding of this process on rocky bodies in our solar system, as well as in other solar systems. Current knowledge of differentiation derives largely from the layers observed via seismology on the Moon. However, the Moon’s much smaller diameter make it a poor analog with respect to interior pressure and phase changes. In this paper we review the current knowledge of the thickness of the crust, the diameter and state of the core, seismic attenuation, heat flow, and interior composition. InSight will conduct the first seismic and heat flow measurements of Mars, as well as more precise geodesy. These data reduce uncertainty in crustal thickness, core size and state, heat flow, seismic activity and meteorite impact rates by a factor of
3
–
10
×
relative to previous estimates. Based on modeling of seismic wave propagation, we can further constrain interior temperature, composition, and the location of phase changes. By combining heat flow and a well constrained value of crustal thickness, we can estimate the distribution of heat producing elements between the crust and mantle. All of these quantities are key inputs to models of interior convection and thermal evolution that predict the processes that control subsurface temperature, rates of volcanism, plume distribution and stability, and convective state. Collectively these factors offer strong controls on the overall evolution of the geology and habitability of Mars.
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