Geophysical Agency Research Articles

UNSUPERVISED MACHINE LEARNING FOR SEISMIC ANOMALY DETECTION: LOCAL OUTLIER FACTOR ALGORITHM TO INDONESIAN EARTHQUAKE DATA

Indonesia's location on the "Ring of Fire" poses a high risk for seismic events. Addressing this, our study applied the Local Outlier Factor (LOF) algorithm for advanced seismic anomaly detection, crucial for geotectonic upheaval prediction. The LOF, adept at unsupervised learning in label-scarce datasets, analyzed data from the Indonesian Meteorology, Climatology, and Geophysical Agency, validated for integrity. Our approach, considering local density deviations, offered a refined alternative to conventional threshold-based detection, accommodating seismic data's intrinsic variability. The LOF algorithm successfully pinpointed anomalies, revealing unique seismic events unconstrained by geography or time. A comparative analysis underscored the LOF's superiority in recognizing local deviations and handling disparate data densities. These findings highlight the LOF's utility in strengthening seismic risk mitigation and anticipatory measures. The diverse anomalies identified, varying in magnitude and depth, reflect Indonesia's complex seismic interplay. To conclude, the LOF proves potent for anomaly detection, potentially elevating public safety and disaster preparedness. Future research will compare the LOF with other unsupervised methods, seeking to deepen seismic risk comprehension

UNSUPERVISED MACHINE LEARNING FOR SEISMIC ANOMALY DETECTION: ISOLATION FOREST ALGORITHM APPLICATION TO INDONESIAN EARTHQUAKE DATA

Indonesia's position on the seismically active Pacific "Ring of Fire" necessitates advanced methods for earthquake detection and preparedness. This paper introduces an application of the Isolation Forest algorithm—an unsupervised machine learning technique—for detecting seismic anomalies in Indonesia's complex geotectonic landscape. Unlike traditional methods that rely on predefined thresholds or patterns, the Isolation Forest algorithm isolates anomalies based on their rarity and distinctness without the need for labeled data. We applied this algorithm to a comprehensive dataset from the Indonesian Meteorology, Climatology, and Geophysical (BMKG) Agency, featuring a decade's worth of seismic events, to identify outliers that may signify potential seismic hazards. Our findings reveal that the Isolation Forest algorithm effectively identifies seismic anomalies, with 874 out of tens of thousands of events flagged as statistically significant outliers. A comparative analysis with traditional seismic anomaly detection models highlights the robustness of the Isolation Forest algorithm in handling the high-dimensional and noisy nature of seismic data, emphasizing its superiority in detecting subtle anomalies

The effect of wind speed in increasing COVID-19 cases in Jakarta: a spatial-temporal analysis from March to September 2020

Background The SARS-CoV-2 virus that causes COVID-19 is described as a highly contagious virus, and wind speed is suspected to be one of the climate elements that play a role in its spread, among others. This study aims to determine the relationship between wind speed and the increase in COVID-19 cases, as well as its potential spread, based on regional characteristics. Methods The design of this study was an ecological study based on time and place to integrate geographic information systems and tested using statistical techniques. The data used were wind speed and weekly COVID-19 cases from March to September 2020. These records were obtained from the special coronavirus website of Jakarta Provincial Health Office and the Indonesian Meteorology, Climatology and Geophysics Agency. The data were analyzed by correlation, graphic/time trend, and spatial analysis. Results The wind speed (maximum and mean) from March to September 2020 tended to fluctuate between 1.43 and 6.07 m/s. The correlation test results between the average wind speed and COVID-19 cases in Jakarta showed a strong positive correlation (r = 0.542; p value = 0.002). Conclusions Areas with high wind speeds tended to show an increase in the number of COVID-19 cases, especially in the coastal areas of Jakarta. Wind speed plays a role in increasing the spread of SARS-CoV-2, in people who did not implement health protocols properly. This mechanism can be worsened with support of environmental factors such as air pollution.

STUDI KESESUAIAN LAHAN POHON SERBAGUNA (MPTS) DI KELURAHAN LAYANA INDAH, KECAMATAN MANTIKULORE, KOTA PALU

This research was motivated by the aftermath of the land rehabilitation program with MPTS plants in the Mantikulore District by the Palu City Government. Closely related to efforts to determine land suitability classes for several types of MPTS in Layana Indah Village, Palu City. Land assessment, especially land suitability assessment, becomes important to prevent obstacles that may arise from limitations for plant growth, especially MPTS plants. The research was carried out for seven months, from April to September 2021, in Layana Indah Village, Mantikulore District, Palu City, Central Sulawesi. The field survey method was purposive sampling or carried out deliberately on other use areas in Palu City, Layana Village. Soil samples were taken from Wintu, representing Layana Village, another use area in the development of forest and land rehabilitation programs. In comparison, collecting climate data from the Meteorology and Geophysics Agency of Palu City. Land suitability assessment refers to the Atlas Format Procedure. Suitability indicators for several types of MPTS (durian, breadfruit, mango and jackfruit) are water availability, field slope, drainage, rock outcrops, and effective depth. The research in Layana Indah Sub-District shows the suitability of MPTS land with the limiting factor of dry months.

Standar Pos Observasi Bulan Kementerian Agama & BMKG (Analisis Terhadap POB. Blang Tiron, Bukit Pole Kompleks Perumahan PT. Perta Arun gas Lhokseumawe)

The implementation of the Rukyat hilal sighting includes an important concern for Muslims. Among the supports for the successful implementation of hilal sightings is the existence of standard and ideal hilal sightings. Based on the author's observations and interviews with reckoning and rukyat staff at the Lhokseumawe Ministry of Religion, POB Blang Tiron Bukit Pole housing complex PT. Perta Arun Gas Lhokseumawe still has not succeeded in seeing the new moon, especially for the sighting of the new moon at the beginning of Ramadan and the beginning of Shawwal (Idul Fitri). So that the POB Bukit Pole Blang Tiron housing complex PT. Perta Arun Gas Lhokseumawe has never printed data on the sighting of the new moon to the Indonesian Ministry of Religion's Hisab Rukyat Agency (BHR). This research uses qualitative methods with the type of research used is field research through direct observation in the field and uses theories taken from the literature in the form of books, journals and others to strengthen research. While the data collection technique uses descriptive analysis method. The research location is located at the Blang Tiron Moon Observation Post, Bukit Pole, Housing Complex of PT. Perta Arun Gas Lhokseumawe. The research results in this study are (1). Natural conditions of the Blang Tiron Bukit Pole Observation Post, Housing Complex of PT. Perta Arun Gas Lhokseumawe apparently has not met the standards set by the Ministry of Religion and the Meteorology, Climatology and Geophysics Agency (BMKG). (2). The success rate of Rukyat Hilal sightings at the POB Blang Tiron Bukit Pole Housing Complex PT. Perta Arun Gas Lhokseumawe still does not meet the average sighting of the new hilal as data on the hilal study spanning four years for the month of Ramadan and Shawwal 1438-1441 H/2017-2020 M.

Analisis Potensi Energi Angin sebagai PLTB di Pantai Watu Ulo Jember Menggunakan data BMKG

This research aims to analyze the potential of wind energy as a resource for Wind Turbine Power Plants (PLTB) in the coastal area of Watu Ulo Beach, Jember. The research adopts a literature review method, utilizing data provided by the Meteorology, Climatology, and Geophysics Agency (BMKG). BMKG data serves as the primary source for this analysis, providing a robust foundation to evaluate the potential of PLTB. The study also focuses on the availability of state-of-the-art technology to optimize the utilization of wind energy, assessing its suitability for the region's characteristics. The research findings are expected to provide a comprehensive overview of the PLTB potential in Watu Ulo Beach, Jember, serving as a basis for the development of sustainable energy infrastructure in coastal areas. The conclusions drawn from this literature review are anticipated to serve as a reference for further research and the implementation of sustainable PLTB projects in the region.

Building Superior Performance with Synergy of Work Discipline, Organizational Culture, and Employee Creativity

Basically, human resources have an important role in every aspect of an organization's life, including government organizations. The purpose of this study is to determine the influence of the influence of work discipline, organizational culture and creativity on the performance of employees of the Office of the Meteorology, Climatology and Geophysics Agency. This research method is associative type with quantitative approach. The study population in question is all employees working at the Office of the Meteorology, Climatology and Geophysics Agency which amounts to 158 people. The sample in this study amounted to 113 respondents. Data collection techniques by means of questionnaires, and data analysis techniques using instrument tests, classical assumption tests, regression analysis, coefficient of determination, tcalculate tests and Fcalculate tests with the help of SPSS 26 Software. The results showed that the results of the hypothesis test obtained a value of Fcalculate > Ftable or 58.963 > 2.69 with a value of Sig. 0.000 < 0.05. So H0 is rejected and H4 is accepted, and it can be concluded that simultaneously the variables of Work Discipline, Organizational Culture and Creativity have a significant effect on Employee Performance at the Head Office of the Meteorology, Climatology and Geophysics Agency.

A Preliminary Results: Study of Crustal Structure in Cimandiri Fault Based on Teleseismic Receiver Function Analysis

West Java is one of the regions in Indonesia that has a complex geological structure caused by plate subduction in the south of Java Island. This resulted the formation structure of the main faults in West Java, including the Cimandiri Fault. The high level of seismicity on the Cimandiri Fault is interesting to be further researched to understand the structure of the Earth crustal, such as variations depth of the Moho layer and the determination of local velocity models of P and S waves. This study used receiver function analysis from teleseismic earthquake data with an epicentral distance of 30°-90° from the station location and magnitude ≥ 6. This study used 3 seismic stations belonging to the Meteorological, Climatological, and Geophysical Agency (BMKG) close to the Cimandiri Fault which are Sukabumi station (SKJI), Warung Kiara (WSJM), and Sukaraja (SSJM). The depth of the Moho layer at SKJI station is 34-36 km, WSJM station is 28-30 km, and SSJM station is 29-31 km which is located close to the segment from the Cimandiri Fault. A negative phase or decrease in speed was observed at the SKJI and WSJM stations which is estimated to come from the Cimandiri Fault structure which is at a depth of 17-19 km. Furthermore, the P wave velocity model at the three stations is at an interval of 7.6-8.6 km/s and the S wave velocity model is at an interval of 4.2-4.8 km/s.

Prototyping of e-fisherman web server to support Indonesian fishermen’s activities

<p>This paper presents a webserver for Indonesian fishermen, to support fishing activities. This is one of the sub-systems of e-Nelayan (in English: eFisherman) architecture, which was connected to e-Nelayan Apps; it helps to provide interaction between two users, including the administrators and fishermen. Using hypertext preprocessor (PHP) language, the website was developed to function on an Apache web server, with the adaptation of my structured query language (MySQL) framework for the database. This system was subsequently divided into two parts: (1) the front-end, which is responsible for the accessibility of data collection and (2) the back-end, where administrators update or modify crucial information: price, fishing result, illegal activity report, save our ship! (SOS) potential fish zone, and ship tracking. The administrators are unable to update the real-time weather information for the front-end part. The application was found to record the information obtained from the fishermen through the e-Nelayan apps and meteorology, climatology, and geophysical agency (BMKG in Indonesian). This web system is expected to carry out the following functions: to ensure easier interactions between fishermen and administrators, to enable easy update of information, to promote monitoring and recording of results, and to ensure fishermen’s safety.</p>

Skillion Roof Design to Get Optimum Solar Radiation in Yogyakarta

Electrical energy is energy that cannot be released from daily activities at home, all elec-tronic equipment requires electrical energy, one source of electrical energy is the electrici-ty company PT. PLN (Persero) and as an alternative source of electrical energy, a home can use solar panels installed on the roof as a small scale power generator or can be called Solar Home System (SHS), but electrical energy obtained is very dependent on the radia-tion received by the solar panels, therefore, to obtain optimum solar radiation, it is neces-sary to calculate the azimuth angle and tilt angle which can be used as a reference for in-stalling solar panels. So mathematical calculations are needed to calculate the maximum azimuth angle and tilt angle. Mathematical modeling is used to calculate solar energy in-stalled at coordinates 7.7° south latitude, in that coordinate, average solar radiation can get from Meteorological, Climatological, and Geophysical Agency on horizontal surface, then calculation the declination angle, latitude angle, hour angle, azimuth angle and tilt angle to get value of incidence angle. Value of the declination angle, latitude angle, and hour angle are constant, while the azimuth angles divide into four directions, it’s 0°, 90°, 180°, and 270° and the tilt angles are 20°, 25°, and 30° on skillion roof design. The results of the calculation and analysis of the movement of the sun for one year show that, by calculating the average solar radiation in a year, the roof of the house in the form of a skillion with an azimuth angle in the 0° gets the most optimal solar energy at an angle of 20° with an aver-age solar radiation of 442,96 W/m2 in one year.

Water Management Program in Telkom University: Planning and Best Practice

This paper discusses the water management conducted by Telkom University, including the fundamental considerations to be taken into account, the implementing organization, the design methods for rainwater systems, and practical experiences in constructing Rainwater Harvesting systems. The management is aware of the conditions and situations related to clean water users, estimates of clean water requirements, potential water sources, and the campus environmental situation. Based on various studies and supported by rainfall data from the Meteorology, Climatology, and Geophysics Agency, a simple calculation was used to derive the design of the Rainwater Harvesting system, which was subsequently implemented. There are several lessons learned from this implementation, including the need for improvements in the foundation structure of soak pits, recommending the construction of ground tanks during the dry season, and the flexibility of ground tank size depending on the availability of funds The abstract should state briefly the purpose of the research, the principal results and major conclusions.

Evaluation of Station Performance of the Indonesian Seismic Network Using the Primary Location Parameter

Abstract Indonesia’s tectonic setting has resulted in a high level of seismic activity, which makes seismic networks and early warning systems vital for this country. Indonesia’s seismic stations, a total of 411 stations in 2021, are maintained by the Meteorological, Climatological, and Geophysical Agency (BMKG). This study attempts to evaluate station performance, because these are crucial in monitoring seismic activity. We utilized information from the BMKG 2020 and 2019 seismic catalogs to analyze the performance of the stations. A total of 13,798 events were reported in 2019 with magnitudes (MLv) of up to 8, whereas 10,163 events with similar magnitudes were reported in 2020. Stations in the eastern part of Indonesia (Sulawesi, Lesser Sunda Islands, the Moluccas, and Papua) detected more events compared to stations in the western part of Indonesia (Borneo, Sumatra, and Java). Up to 1651 events were detected by a single station in eastern Indonesia, compared to 847 events in western Indonesia. BMKG stations in eastern Indonesia have recorded ample amounts of events, which is consistent with the high seismic activity found there. In terms of station coverage, events in the eastern part have better station coverage due to smaller azimuthal gaps, considering the geographic location. We also analyzed station performance and the number of recorded stations in terms of a function of time for each event in the Sumatra, Sulawesi, Lesser Sunda Islands, and Papua regions. Although the number of recordings obtained by stations was high after 15 s since the origin time, the azimuthal gap progression in Sumatra and Java remained large. Therefore, an additional ocean-bottom seismometer needs to be installed in the Sumatra–Java trench.

Analyzing Seismicity Pattern of the Gorontalo Region and Its Surroundings in the Form of Hypocenter Relocation Using Double Difference Method

The level of seismic activity due to earthquake events in Gorontalo is strongly influenced by the tectonic system model of the Gorontalo region and the presence of a subduction zone in the Sulawesi Sea. These characteristics make the Gorontalo region have high seismic activity. To describe the pattern of seismicity in the Gorontalo region, it is necessary to conduct an analysis in the form of earthquake hypocenter relocation using the double difference (hypoDD) method. This method uses residual travel time data from each pair of hypocenters to the recording station. This study aims to analyze the results of hypocenter relocation and describe the subsurface model related to the seismicity pattern of Gorontalo and its surroundings. The data used are P and S waves for 7 years recorded at the Meteorology, Climatology and Geophysics Agency (BMKG) station. The earthquake hypocenters relocated in this study were 3,940 out of 4,598 earthquake events. The results of hypocenter relocation show a fairly good seismicity pattern obtained from good RMS values and distribution patterns following Gorontalo tectonic patterns. In general, the seismicity pattern of Gorontalo and its surroundings is strongly influenced by activity in the Sulawesi Sea subduction zone and the Gorontalo fault in the region. The seismicity caused by the subduction zone has a depth of 50 - 200 km, and due to the active faults in the Gorontalo region has a depth of 2 - 25 km.

MICE Implementation to Handle Missing Values in Rain Potential Prediction Using Support Vector Machine Algorithm

Support Vector Machine (SVM) is a machine learning algorithm used for classification. SVM has several advantages such as the ability to handle high-dimensional data, effective in handling nonlinear data through kernel functions, and resistance to overfitting through soft margins. However, SVM has weaknesses, especially when handling missing values in data. The use of SVM must consider the missing values strategy chosen. Missing values in data mining is a serious problem for researchers because it causes many problems such as loss of efficiency, complications in data handling and analysis, and the occurrence of bias due to differences between missing data and complete data. To overcome the above problems, this research focuses on understanding the characteristics of missing values and handling them using the Multiple Imputation by Chained Equations (MICE) technique. In this study, we utilized secondary data experiments that contain missing values from the Meteorological, Climatological, and Geophysical Agency (called BMKG) related to predictions of potential rain, especially in DKI Jakarta. Identification of types or patterns of missing values, exploration of the relationship between missing values and other variables, incorporation of the MICE method to handle missing values, and the Support Vector Machine Algorithm for classification will be carried out to produce a more reliable and accurate prediction model for rain potential. It shows that the imputation method with the MICE gives better results than other techniques (such as Complete Case Analysis, Imputation Method Mean, Median, Mode, and K-Nearest neighbor), namely an accuracy of 89% testing data when applying the Support Vector Machine algorithm for classification.

Analysis of Seismotectonic Parameters and Earthquake Return Periods in The Nias Area (1980-2021)

The Nias Islands region is an area prone to earthquakes with a very high level of earthquake activity. One reason is the source of the subduction zone which is in the northwest of the Nias Islands. The aim of this work is to determine the b-value, seismic index, and earthquake return period using probabilistic techniques. For the years 1980 to 2021, the Meteorology, Climatology and Geophysics Agency (BMKG) published data with a magnitude of 3-6.7 and a depth (H) of 10-300 Km. The research results obtained by calculating the highest b-value is 0.791 in South Nias district and the highest a-value is in the South Nias district of 3.97. Calculation of the highest seismicity index with a magnitude of 6.7 in South Nias district with a-value of 7.223191 with an earthquake return period of 14 years.

Risk factors, logistic model, and vulnerability mapping of lumpy skin disease in livestock at the farm level in Indragiri Hulu District, Riau Province, Indonesia, in 2022.

Lumpy skin disease (LSD) is an emerging epidemic in livestock in Indonesia. It was first reported in the Indragiri Hulu Regency of Riau Province, which has more cases than the surrounding regencies. This study aimed to identify the risk factors and generate a logistic regression model and vulnerability map of LSD in the Indragiri Hulu Regency. We used a structured questionnaire to interview the case and control farm owners to evaluate the risk factors. We evaluated 244 samples, consisting of 122 case and control farm samples each. At the cattle farm level, the risk factor data related to LSD were analyzed using descriptive statistics, bivariate analysis with Chi-square, and odds ratio, while the logistic model was derived using multivariate logistic regression analysis. Using variables, such as the number of cases and risk factor variables included in the model logistic, and the temperature, humidity, and rainfall data from the Meteorology, Climatology, and Geophysical Agency, we analyzed the vulnerability map of LSD in the regency using scoring, weighting, and overlay methods. Ten significant risk factors were associated with LSD occurrence. The LSD model obtained from the logistic regression analysis was LSD (Y) = -3.92095 + 1.13107 (number of cattle >3) + 1.50070 (grazing cattle together with other farmers' cattle) + 1.03500 (poor management of farm waste/dirt) + 2.49242 (presence of livestock collectors/traders near the farm location) + 1.40543 (introduction of new livestock) + 2.15196 (lack of vector control measures on the farm). The LSD vulnerability map indicated that the villages with high vulnerability levels were Rantau Bakung, Kuantan Babu, and Sungai Lala in the Rengat Barat, Rengat, and Sungai Lala subdistricts, respectively. We found 10 significant risk factors associated with LSD occurrence. The LSD model included the number of cattle (>3), cograzing with other farmers' cattle, poor management of farm waste/dirt, the presence of livestock collectors/traders near the farm, introduction of new livestock, and lack of vector control measures on the farm. The LSD vulnerability map indicated that villages with high vulnerability levels included Rantau Bakung in the Rengat Barat subdistrict, Kuantan Babu in the Rengat subdistrict, and Sungai Lala in the Sungai Lala subdistrict.

Extreme Drought Assessment in Sumatra-Indonesia Using SPI and EDI

Even though Sumatra is very vulnerable to the effects of drought, research identifying drought on this island is very limited, especially extreme drought. This research was conducted to identify extreme drought in Sumatra using the Standardized Precipitation Index (SPI) and the Effective Drought Index (EDI). This study uses precipitation data from the Indonesian Meteorology, Climatology and Geophysics Agency (BMKG) and Global Precipitation Climatology Center (GPCC) reanalysis data. The composite indices were conducted to discover some phenomena that cause the drought based on El Niño and positive Indian Ocean Dipole (IOD) events. The results showed that the El Niño and positive IOD phenomena were more likely to influence extreme droughts. However, the droughts in 2014 and 2008 tended to be influenced by the negative Sea Surface Temperature anomaly (SSTA). The spatial analysis results show that the areas that experience extreme drought more often are the west coast of Sumatra (except Aceh province), especially based on SPI12 and EDI. The composite indices results show that the drought that occurred in Aceh province was more influenced by the El Niño phenomenon in the December-January-February (DJF) period and the positive IOD in the June-July-August (JJA) – September-October-November (SON) period. In addition, Aceh province is an area that is not affected by El Niño-positive IOD, especially during the SON-DJF period. These results can be used to mitigate drought, especially when El Niño-positive IOD phenomena cause it.

Hybrid Radio over Fiber with Radio over Free Space Optic for 5G Fronthaul Network Implementation in Urban Areas

Optical fiber can meet the demand for fronthaul on 5G networks that offer high bandwidth, large capacity, high data rate and is free from electromagnetic interference. However, deploying infrastructure faces issues like permits and high costs. Hybrid Radio over Fiber (RoF) technology with Radio over Free Space Optic (RoFSO) can be a solution in urban areas, where the installation requires high costs. This research investigates a hybrid RoF-RoFSO scheme at a frequency of mmWave 26 GHz by considering atmospheric attenuation values arising from meteorological effects, such as rain, smog, and dust, using Optisystem. This research considers QPSK, 16-QAM, and 64-QAM modulation schemes, distance variations on the FSO and the meteorological data from the Indonesian Meteorology, Climatology and Geophysics Agency (BMKG) from March 2022 to May 2022. The results show that attenuation due to high rainfall is the main cause of signal quality degradation and limits the transmission distance on the FSO link. The maximum distance is 600 m using the QPSK and 16-QAM modulation schemes, while for the 64-QAM modulation scheme, the maximum transmission distance is 500 m. Meanwhile, damping values caused by foggy and dusty conditions can reach distances of up to 1000 m for the three modulation schemes.

Effect of mulch weight on temperature, soil moisture and vegetative growth of Sigambiri Merah in lowlands

Rice is staple food source for most Indonesians. However, highland rice development on dry land is regularly isolated by action makers who find it simple to development paddy construction. One of the cultivation techniques to achieve maximum production of upland rice in dry land is by modifying the microclimate in the roots zone using organic mulch. The study was carried out at the Experimental Farm of Meteorology, Climatology and Geophysics Agency, Sempali, Medan. The research method is a non-factorial randomized block design with three replications. Mulch thickness (M) used as treatment, consisted of without mulch (M0), 20 t/Ha (M1), 25 t/Ha (M2), and 30 t/Ha (M3). Observations were invented insanely by expansive two fragment for each analysis 28 days after planting (DAP). As a result, we found that multi-weight is efficient in reducing soil temperature and increasing soil moisture compared to without mulch, but there is no improvement in the vegetative growth of Sigambiri Merah because it was still in the early stages of rice growth.

Groundwater recharge estimation using chloride mass balance method on the southern slope of Merapi Volcano, Indonesia

Groundwater is a main resource for the majority of Indonesian people as a source of clean water to meet their daily needs. The increase in groundwater use is unavoidable due to increasing development in Indonesia, especially in Yogyakarta. Groundwater recharge is important in the hydrological cycle to meet groundwater needs. Therefore, this study aims to estimate groundwater recharge by the chloride mass balance (CMB) method on the southern slope of Merapi Volcano in Yogyakarta, Indonesia. This research was conducted in the rainy and dry seasons from August 2022 until January 2023. This research collects annual rainfall near the study area from the Meteorology, Climatology, and Geophysics Agency (BMKG) Yogyakarta station, monthly data collected from eighteen samples of groundwater station, and monthly data collected from fifteen samples of rainwater in the study area. The chemical content of groundwater and rainwater samples is analyzed using argentometry to obtain chloride concentration. The result of annual rainfall in the study area is 3,603.878 mm/year. The average chloride concentration in rainwater is 1.1 mg/L, while the average chloride concentration in groundwater is 8.015 mg/L. The CMB method calculation showed that the recharge in the study area ranges from 171.65 to 1,711.29 mm/year. The groundwater recharge has a positive correlation with elevation and rainfall. High groundwater recharge is also found in the northern area due to fractured lava aquifer.