the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Mid-field tsunami hazards in greater Karachi from seven hypothetical ruptures of the Makran subduction thrust
Abstract. New Makran simulations imply two generalized zones of mid-field tsunami hazard in greater Karachi. The simulations presuppose seven megathrust ruptures that strike east-west, range in area from 100 × 150 km to 355 × 800 km, and lie west of the city by no less than 100 km. The assumed seismic slip is uniform across each rupture area. The smallest rupture approximates the 1945 Makran earthquake of magnitude 8.1, while the largest corresponds to a previously conjectured giant Makran earthquake of magnitude 9.2. None of the sources include a complication in 1945: late-arriving waves from submarine slides or splay faulting. Consequently, the first simulated wave is the largest in each of the seven scenarios. And because the sources are to the west, the simulated waves are higher, and arrive sooner, at Karachi Port (1.5 hr) than 30 km farther east at Port Qasim (nearly 3 hr). These combinations of height and arrival time can be generalized as properties of two hazard zones: a western one that includes Karachi Port, and an eastern one that includes Port Qasim. The simulated flooding extends farthest inland into low-lying residential areas of the western zone. Neither hazard zone is near-field or far-field. That is, neither is near enough to the fault ruptures for felt seismic shaking to dependably warn of a fast-arriving tsunami, yet neither is distant enough to receive more than three hours of advance notice through tsunami warning systems. Our simulations are intended to support emergency management in this mid-field setting.
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Status: open (until 15 Aug 2024)
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RC1: 'Comment on nhess-2024-110', Anonymous Referee #1, 22 Jul 2024
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Comments
The article examines tsunami hazards in the greater Karachi area resulting from seven hypothetical ruptures of the Makran subduction thrust, identifying two primary hazard zones: one near Karachi Port and the other adjacent to Port Qasim. Through numerical modeling, it is demonstrated that larger ruptures produce higher waves and faster arrival times, thereby highlighting the central region's susceptibility due to its low elevation and critical infrastructure. The study emphasizes the necessity of early warning systems and preparedness strategies to mitigate tsunami risks in this region.
Overall, the paper is well-written, the methodology is robust, and I appreciated the way the results were presented. However, I have some comments and recommend a minor revision before publication:
- Discussion of Results: The paper lacks sufficient discussion regarding the results, particularly in comparing the actual Karachi marigram with the simulated results. Other studies have presented more robust simulations between the real data from the 1945 tsunami and their results. The authors should indicate that the discrepancies between their findings and the actual 1945 tsunami waveform may come from their simplistic representation of the tsunami source. The differences observed between the simulations and the two marigrams may not solely be attributed to tide gauge errors, but also to our limited understanding of the 1945 tsunami source.
- Title Adjustment: I recommend removing the word "seven" from the title.
- Abstract Corrections: In Abstract (line 13), "km" should be corrected to "km²." Additionally, in line 21, the repeated use of "neither" makes the text unnecessarily verbose.
- Typos and References: The manuscript contains several typographical errors, such as "Tohuku" (which should be "Tohoku") and "20011" (which should be "2011"). Moreover, in several instances, the authors have neglected to include the publication year of references in parentheses. A thorough review of the text for typos and potential grammatical errors is recommended.
- Figure Combination: It appears that Figures a&b could be combined into a single figure unless additional details (e.g., an earthquake catalog) are added to panel (a).
- Model Details: Additional information about the GeoClaw model should be included, such as inputs and outputs, the types of water equations used, the algorithms employed for inundation calculations, the nature of the friction effects (whether constant or variable), and whether structured or unstructured grids are used.
- Font Size in Figures: The font size in Figure 2 should be increased for better visibility.
- Scenario Simplifications: More details are needed regarding the simplifications made in selecting scenarios. Such simplifications (e.g., rectangular sources and uniform slip) could lead to potentially underestimated or less complex wave height distributions. The strike angle of 270 degrees appears inconsistent with the tectonics of the Makran thrust; any alterations in the strike direction could yield different wave directions and results. These simplifications require a more thorough explanation. Furthermore, these scenarios do not seem to offer new insights compared to those proposed in previous studies.
- Table A3 Enhancements: In Table A3, please add an additional column indicating the moment magnitude (Mw) for each scenario.
Citation: https://doi.org/10.5194/nhess-2024-110-RC1 -
AC1: 'Reply on RC1', Haider Hasan, 07 Aug 2024
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Thank you for your comments and suggestions regarding our manuscript titled "Mid-field tsunami hazards in greater Karachi from seven hypothetical ruptures of the Makran subduction thrust." We appreciate the time and effort you have taken to review our work. In response to your comments, we have carefully addressed each point. A detailed reply to each comment is attached.
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