# Next-Generation EEW Empowered by NDSHA: From Concept to Implementation

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## Abstract

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## 1. Introduction

_{c}) and Pd [22], (3) the introduction of home seismometers and the crowdsource earthquake early warning [23,24]. Even though it is charged with uncertainties (e.g., magnitude estimation [25]), EEW has been implemented in various infrastructures and is playing an active role, e.g., for transport lines [26], dams [27], buildings [28,29], and expressway [30].

## 2. Earthquake Early Warning (EEW)

#### 2.1. Limits of Current EEW

#### 2.2. Next-Generation of EEW (Regional EEW + SHA)

#### 2.2.1. From Concept to Real Implementation

_{MMI}= VI) and to a factory (estimated I

_{MMI}= VII). The hospital is supposed to take an emergency response to protect lives to the most possible extent, but the factory could choose to continue production activities if the engineering structure was designed to cope with I

_{MMI}= VII; the losses are minimized in this case.

#### 2.2.2. Improvement and Alternative

## 3. NDSHA Approach: Methodology

## 4. EEW2.0

#### 4.1. Simple Classification of Earthquakes, and Their Damaging Potential, from Magnitude

#### 4.2. Hazard Database: MMI Maps

^{6}possible combinations) at the simple cost of spending some time. Similarly, though, we cannot precisely predict the location and size of the next damaging earthquake linked to XSH, we can consider all the relevant possible sizes (M $\ge $ 5.0) and locations of potential earthquakes according with now-available geophysical datasets, and then model all the possible ground motion values at the simple cost of using more memory and computing resources.

_{design}= 8.7 was used in each seismogenic node prone to great earthquakes and only one node is included (Figure 7). Following the source gridding rule, in the source area there are $16\times 17=272$ $0.2\xb0\times 0.2\xb0$ cells (Figure 7). For example, the cells numbered 1st~16th occupy the first row, 17th~32nd occupy the second row, and the last cell is the 272nd. In order to take all possible earthquake scenarios into consideration, 12 simplified regional computations are performed in 272 cells, with the following procedures:

- (1)
- The seismogenic zone is defined by the coordinates 99.6°~102.8° E, 28.8°~32.2° N, i.e., the whole XSH.
- (2)
- The source is placed in the first cell (99.6°~99.8° E, 32.0°~32.2° N), and its magnitude is set as 5.0.
- (3)
- All the 272 (smoothed) sources related with XSH are characterized, for simplification of computing procedures, by the same rupture and the focal mechanism characteristic of XSH (strike = 146°, dip = 82°, rake = 349°).
- (4)
- The predefined 0.2° × 0.2° cellular grid, corresponding to the cellular structural models referenced by [45], is adopted for the computation of synthetic seismograms at the sites.
- (5)
- For the same source cell defined in (2), the value of magnitude is changed to the next class, and the depth is defined following the predefined rules, iterating for the next 11 (up to the final magnitude class) regional computations in (3).
- (6)
- The magnitude is reset to 5.0 (and the depth to 10 km), the source is moved to the 2nd source cell (99.8°~100.0° E, 32.0°~32.2° N), and steps (2)–(4) are repeated.

#### 4.3. Decision Framework for Alert Notification

_{s}7.5 happens and the warning alert is rapidly sent to a town, but the general population does not understand the meaning of the warning alert, just a few resulting emergence responses are activated: the earthquake still severely affects the normal life in the town. This situation may be more common in the countries and regions where EEW is progressing or planning. For the effective protection of lives and reduction in damages and losses, it is mandatory to consider potential damages and losses, and to compare them with losses caused by false alarms. For example, a factory owner may be more interested in the comparison between the losses resulting from downtime (production interruption) after receiving an alert and the losses resulting from damages resulting from ignoring the alert. Accordingly, it is necessary to differentiate warning alert to different end-users at different sites or situations, so that they could have suitable emergence responses to the alert, e.g., a surgery room cannot ignore an I

_{MMI}= 5 alert because slight ground motion could still severely influence the high resolution and complex surgery, but a school designed against I

_{MMI}= 6 could ignore it and continue its normal actions in a short time.

#### 4.4. Conceptual Working Mechanism

_{1}is the distance between the epicenter and the closest station. R

_{2}is the radius of the blind zone (i.e., the distance that seismic wave travels in the time it takes to detect and process seismic signals until the magnitude and epicenter are determined). The grid stands for the protected area by the early warning alert. Each yellow point stands for the a priori computed MMI value at each site. Indicating the average P-wave velocity with V

_{p}and the average S-wave velocity with V

_{s}, and the epicenter distance to one targeted site with EDI (i.e., the thick black line in the figure), the theoretical leading time T

_{wt}(i.e., ignoring the time delay that may be caused by data processing, transmission, etc.), in each site of the protected area is:

## 5. Discussion and Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**The study area of EEW2.0. The red grid, covering 99.6°~102.8° (E) and 28.8°~32.2° (N), shows the area where the scenario earthquakes are considered. The irregular black polygon enclosing part of the red cells stands for the Xianshuihe Fault Zone (XSH). The black lines stand for segments of XSH [34]. It can be clearly seen that the red grid covers the four vertices of the irregular polygons surrounding XSH. The yellow circle stands for the seismogenic node prone to $M\ge 8.2$ earthquakes [35]. The blue pushpins stand for the residential areas, and Chengdu, Lushan, Kangding, Wenchuan, Beichuan, Daofu, Luhuo, and Ganzi are indicated by black dots. The approximate location of the planned Sanba Nuclear Power Plant is marked by a pierced yellow circle. The approximate location of the Sichuan-Tibet railway is also displayed.

**Figure 4.**The differences of MMI values obtained considering computations of four scenarios with varying magnitude values (magnitude step is equal to 0.5) whereas the other focal parameters are fixed. Distribution of differences between (

**a**) magnitude 7 and 6.5, and (

**b**) magnitude 7.5 and 7.0 scenario computations. The green triangles indicate the different is zero.

**Figure 5.**The differences of MMI values obtained considering computations of four scenarios with varying magnitude values (magnitude step is equal to 0.2/0.3) whereas the other focal parameters are fixed. Distribution of differences between (

**a**) magnitude 6.7 and 6.5, (

**b**) magnitude 7.0 and 6.7, (

**c**) magnitude 7.2 and 7.0, and (

**d**) magnitude 7.5 and 7.2. The green triangles indicate the different is zero.

**Figure 6.**The differences of MMI values obtained from four scenarios with varying levels of magnitude (magnitude step is equal to 0.1), whereas the other focal parameters are fixed. Distribution of differences between (

**a**) magnitude 7.1 and 7.0, and (

**b**) magnitude 7.2 and 7.1 scenario computations. The green triangles indicate the different is zero.

**Figure 7.**Study area with “protected” and “seismogenic” zone (28.8°~32.2° N, 99.6°~102.8° E) meshed by 0.2° × 0.2° grid. For each cell of the protected area, 12 MMI maps are computed.

**Figure 8.**The framework of MMI Database (MMID, shortened as ID) to be used in the EEW2.0. The establishment of an integrated ID could be divided into three steps: (1) Grid the whole protected area with 0.2° × 0.2° grids; (2) assign a unique label to each cell, i.e., CEmn, 1≤m, n≤16, and m, n are always integers. For example, CE11 stands for the cell at the first row and the first column, and CE1338 stands for the cell at the 13th row and the 38th column. (3) At each cell, two fields are assigned. The first field is location, including the longitude and latitude range; the second field is the classification of magnitudes. For example, in the cell CE11, the classification of magnitudes includes four classes, i.e., M1, M2, M3, M4 (maybe more, in practice). Each magnitude class refers to a unique prepared MMI result labeled by INTmnX, matching the unique MMI result prepared for the Xth magnitude class in the cell at the mth row and the nth column, e.g., assumed an M = 7.0 earthquake occurred in CE11, and 7 is in M3 class, then the earthquake could quickly match the prepared MMI result INT113 in the MMI database.

**Figure 9.**The sources to be used in the 12 scenario computations, with a different value of magnitude for each cellular earthquake source. For each scenario computation, the value of magnitude is defined as the lower limit of the corresponding magnitude, e.g., the adopted magnitude for computing MMI map is 5.0 for the 5.0 ≤ M < 5.5 class.

**Figure 11.**Suggested decision framework for the end-user (i.e., a factory in this case) to determine whether to issue an alert after an earthquake is detected.

**Figure 12.**The conceptual view of EEW2.0. The red solid circle located in (1,1) stands for the epicenter, and R

_{1}is the distance between the epicenter and the closest station. R

_{2}is the radius of the blind zone (i.e., the distance that seismic wave travels in the time it takes to detect and process seismic signals until the magnitude and epicenter are determined). The rectangle filled with orange circles, in 0.2° × 0.2° cells, stands for the protected area. Assuming the average P-wave velocity is V

_{p}and the S-wave velocity is V

_{s}, and the epicenter distance to one target site is EDI (i.e., the thick black line in the figure), the warning time T

_{wt}in each cell is: T

_{wt}= EDI ∗ (1⁄V

_{s}− 1⁄V

_{p}) − T

_{detect}− T

_{processing}. T

_{detect}means the time needed at the closest station to detect the earthquake signal and T

_{processing}is the time needed to estimate magnitude and epicenter. The orange circles stand for the precomputed Modified Macroseismic Intensity (MMI) by NDSHA (e.g., [43]).

**Figure 13.**One possible application scenario of MMI database: (

**A**) Fast estimation of magnitude and epicenter; (

**B**) fast matching of the cell including the epicenter and the magnitude class; (

**C**) extraction from the MMI database of the pertinent MMI maps and issue of the warning to different end users, e.g., school, hospital, residential building, factory, and train.

Earthquake Early Warning | Seismic Hazard Assessment Tools (PSHA, NDSHA) | |
---|---|---|

Purposes | Reduction in Seismic Risk | |

Time length | After earthquakes, a few seconds to a few tens of seconds [46] | Before earthquakes, long- to intermediate-term prediction (PSHA: ≥50 years, e.g., [47]; NDSHA: from a few years to tens of years, e.g., [43]) |

Input | First seconds of primary P waves | Historical earthquake catalogue, seismogenic zones, structural models (only for NDSHA), focal mechanism (only for NDSHA), seismogenic nodes (only for NDSHA) |

Output | Lead time and estimated ground motion values | Seismic hazard in terms of probabilistic-based or deterministic-based ground motion values |

Advantages | Prepare time for emergence responses | Prepare descriptions for future seismic hazard distribution |

Disadvantages | Missed or false alarms [48], blind zones | Underestimation and nonphysical-based (PSHA, e.g., [49]) |

**Table 2.**Magnitude classes used in computing MMI database. Each class could be simply expressed as XX, where the first X stands for I, II, and III, and the second X stands for A, B, C, D, and E. For example, IA refers to the magnitude class 5.0 ≤ M < 5.5.

Class | $\mathbf{I}:\text{}5.0\le \mathit{M}7.0$ | $\mathbf{II}:\text{}7.0\le \mathit{M}8.0$ | $\mathbf{III}:\text{}\mathit{M}\ge 8.0$ |
---|---|---|---|

A | $5.0\le M<5.5$ | $7.0\le M<7.2$ | $8.0\le M<8.2$ |

B | $5.5\le M<6.0$ | $7.2\le M<7.4$ | $8.2\le M<8.4$ |

C | $6.0\le M<6.5$ | $7.4\le M<7.6$ | $8.4\le M<8.6$ |

D | $6.5\le M<7.0$ | $7.6\le M<7.8$ | |

E | $7.8\le M<8.0$ |

Class | Magnitude | Earthquake Effects |
---|---|---|

Minor | 3.0~3.9 | May be felt |

Light | 4.0~4.9 | Likely felt |

Moderate | 5.0~5.9 | Minor damage may occur |

Strong | 6.0~6.9 | Damage may occur |

Major | 7.0~7.9 | Damage expected |

Great | 8.0 or larger | Significant damage expected |

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**MDPI and ACS Style**

Zhang, Y.; Wu, Z.; Romanelli, F.; Vaccari, F.; Jiang, C.; Gao, S.; Li, J.; Kossobokov, V.G.; Panza, G.F. Next-Generation EEW Empowered by NDSHA: From Concept to Implementation. *Geosciences* **2021**, *11*, 473.
https://doi.org/10.3390/geosciences11110473

**AMA Style**

Zhang Y, Wu Z, Romanelli F, Vaccari F, Jiang C, Gao S, Li J, Kossobokov VG, Panza GF. Next-Generation EEW Empowered by NDSHA: From Concept to Implementation. *Geosciences*. 2021; 11(11):473.
https://doi.org/10.3390/geosciences11110473

**Chicago/Turabian Style**

Zhang, Yan, Zhongliang Wu, Fabio Romanelli, Franco Vaccari, Changsheng Jiang, Shanghua Gao, Jiawei Li, Vladimir G. Kossobokov, and Giuliano F. Panza. 2021. "Next-Generation EEW Empowered by NDSHA: From Concept to Implementation" *Geosciences* 11, no. 11: 473.
https://doi.org/10.3390/geosciences11110473